# Battery Fuse Blocks



## Sunking (Aug 10, 2009)

Si I assume no one uses Over Current Protection?


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## major (Apr 4, 2008)

Sunking said:


> Si I assume no one uses Over Current Protection?


The MRBF fuses are marine jobs rated at 58V, so not many of us here are familiar with them or use those or similar types. We have had many fuse and fuse holder (or fuse block) discussions over the years. Controller manuals typically recommend the appropriate fuse for the user.


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## Sunking (Aug 10, 2009)

Thanks Major but I am looking for something to install directly onto the battery post. Perhaps there is nothing for that high of voltage, that is why I am asking. 

Bit concerned putting a OCPD downstream from the source as it leaves cable unprotected. I come from the NEC world where all sources shall be protected at the source. The controller is not the source, it is a utilization device in my world.


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## major (Apr 4, 2008)

Sunking said:


> Thanks Major but I am looking for something to install directly onto the battery post. Perhaps there is nothing for that high of voltage, that is why I am asking.
> 
> Bit concerned putting a OCPD downstream from the source as it leaves cable unprotected. I come from the NEC world where all sources shall be protected at the source. The controller is not the source, it is a utilization device in my world.


In EVs, the fuse is typically located (or recommended to be located) in the battery box or adjacent to it. It is further recommended that in cases where multiple battery boxes are used, a fuse be installed in each. We do see some installations where the fuse is installed near the controller, but this is DIY, remember


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## dladd (Jun 1, 2011)

It is the fear of over stressing the battery terminal due to NVH issues while driving that has most of us putting the fuse a short distance from the terminal instead of on the terminal itself.


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## Ziggythewiz (May 16, 2010)

I didn't respond because I don't understand how those blue sea blocks work. Looks more like a fuse connector than a holder.

Are you sticking them off every battery or just one or two? 

Near the battery is good but where most people only have a fuse or two anyway it's not like they can be close to every source.

My fuse and holder is this style:


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## Sunking (Aug 10, 2009)

Ziggythewiz said:


> I didn't respond because I don't understand how those blue sea blocks work. Looks more like a fuse connector than a holder.


Bolted directly to the battery post or term plates. They come in either 1 or 2 hole models using 3/8" bolts on 1-inch centers. If you had one in your hand you would understand quickly.

The bottom piece is a copper zinc coated buss bar with either 1 or 2 insulated studs. The fuses are the square looking things. Perhaps this will help. They are good up to 600 amps. But as Major indicated are limited to 60 volts. I use them in off-grid solar applications and a modified golf cart. Fits like a glove on a T-105.


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## Ziggythewiz (May 16, 2010)

Yes, that helps. I thought that might be the case ("square looking things") but since the site said fuses not included I thought maybe those were just clamping plates or something.


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## major (Apr 4, 2008)

Sunking said:


> Bolted directly to the battery post or term plates. They come in either 1 or 2 hole models using 3/8" bolts on 1-inch centers. If you had one in your hand you would understand quickly.
> 
> The bottom piece is a copper zinc coated buss bar with either 1 or 2 insulated studs. The fuses are the square looking things. Perhaps this will help. They are good up to 600 amps. But as Major indicated are limited to 60 volts. I use them in off-grid solar applications and a modified golf cart. Fits like a glove on a T-105.


Looks like a fastener failure waiting to happen


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## Sunking (Aug 10, 2009)

major said:


> Looks like a fastener failure waiting to happen


None yet using 3/8 locking hardware. As good as anything I have seen here or on any controller. Personally I use two-hole versions which is almost impossible to loosen up.


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## major (Apr 4, 2008)

Sunking said:


> None yet using 3/8 locking hardware. As good as anything I have seen here or on any controller. Personally I use two-hole versions which is almost impossible to loosen up.


How can you get a tight clamp on the high current lug contact without compressing an insulator? And that will fail, eventually. And then the whole strain relief problem. I hate to see fuses hung off other components, like batteries and contactors and such. I've said this many times on this board.....Use the proper fuse with the proper fuse block.

Kinda academic anyway talking about a 58V fuse


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## Sunking (Aug 10, 2009)

major said:


> How can you get a tight clamp on the high current lug contact without compressing an insulator?


You do not compress the insulator, all the mechanical strain is on the MRBF fuse which is made for it. I would send you one to look at but they are expensive. 

I am asking what you guys use at the source. I have my answer. You do not use anything at the source. YOu take your chances. Got it loud and clear.


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## major (Apr 4, 2008)

Sunking said:


> You do not compress the insulator, all the mechanical strain is on the MRBF fuse which is made for it. I would send you one to look at but they are expensive.
> 
> I am asking what you guys use at the source. I have my answer. You do not use anything at the source. YOu take your chances. Got it loud and clear.


What is putting the fuse in the battery box if not the source?


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## palmer_md (Jul 22, 2011)

I agree. The battery box is the source, not the individual cells. If you have a fuse inside the box on the line leading out of the box you are fused at the source. Otherwise you need to put a fuse on every cell.


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## Sunking (Aug 10, 2009)

major said:


> What is putting the fuse in the battery box if not the source?


Is the fuse or device installed directly one the battery post, or is it a pig tail cable with a terminal like a ring from the battery post to a fuse block? I think I already have my answer. 

All I am looking for is any other Battery Fuse Block that mounts directly to a battery post. I am not asking for EV particularly. I just asked here if there was a batter mouse trap than a MRBF or AGM fuse. I do telecom battery plants and solar professionally which is mostly 48 volt and lower. Well actuaslly more than that when it comes to AC and DC distribution, UPS, power distribution. You get the idea. As a hobby I mess with Golf Carts and NEV, but again those are typically 48 and some 60 volt stuff.

I am not trying to step on your guys toes, just looking to see if there is something better out there and thought EV might be a good place to look.

I also assume you have to fuse both polarities since the system is not bonded?


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## Ziggythewiz (May 16, 2010)

Sunking said:


> I also assume you have to fuse both polarities since the system is not bonded?


A fuse doesn't care about polarity. If you have a short that means the fuse is seeing both.

You should have one per battery box, but unless you have one per battery on post or off post is irrelevant.


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## major (Apr 4, 2008)

Sunking said:


> Is the fuse or device installed directly one the battery post, or is it a pig tail cable with a terminal like a ring from the battery post to a fuse block? I think I already have my answer.


It is a bad idea to hang the fuse directly off the battery terminal or off the terminal of any other component other than the fuse block designed to hold that particular fuse.

This is DIY so you can find all sorts of installations. You can put your fuses where you want to. But don't infer the way I describe is incorrect or otherwise less than the best method to wire an EV.


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## Sunking (Aug 10, 2009)

Ziggythewiz said:


> A fuse doesn't care about polarity. If you have a short that means the fuse is seeing both.
> 
> You should have one per battery box, but unless you have one per battery on post or off post is irrelevant.


Sorry but unless the one polarity or the other is bonded to the frame, putting a fuse on only one polarity is useless. There has to be a return path or complete circuit for fault current to flow. 

That is why commercial and industrial system use Delta aka non grounded system. They cannot afford outages from unnecessary line faults. Grounded system are unreliable and dangerous prone to outages. In non grounded system you can have a ground fault in any single circuit conductor and nothing happens except an alrm goes off alerting maintenance personnel there is a ground fault and to schedule a controlled shut down for repairs. 

All EV's I know of use floating systems, both polarities have to be fused or some sort of Ground Fault Protection Device has to be employed. A ground fault on any single polarity, nothing should happen except an alarm and orderly shut down. If an EV used a ground system, hundreds of people would be hurt or killed from electrocution. Not to mention some huge arc explosions.


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## Sunking (Aug 10, 2009)

major said:


> It is a bad idea to hang the fuse directly off the battery terminal or off the terminal of any other component other than the fuse block designed to hold that particular fuse.


I think we have a communication problem Houston.

Have you ever seen battery term plates? The kind that are 1/4 inch thick with 2 hole terminations that use 5/8 inch bolt hardware to support multiple 750 MCM cables that weigh a hundred pounds or more? Basically they are buss bars. I do not think we are on the same page.

These are the kind of batteries I work with, and these are small ones.


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## Ziggythewiz (May 16, 2010)

Sunking said:


> I think we have a communication problem Houston.


This is Houston. We concur on the communication failure. Jettison the thread immediately.


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## evmetro (Apr 9, 2012)

Major, we may not agree on everything, but I sure like how you are able to grasp the concept of DIY. Not many folks with your background are bilingual this way.


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## major (Apr 4, 2008)

Sunking said:


> I think we have a communication problem Houston.
> 
> Have you ever seen battery term plates? The kind that are 1/4 inch thick with 2 hole terminations that use 5/8 inch bolt hardware to support multiple 750 MCM cables that weigh a hundred pounds or more? Basically they are buss bars. I do not think we are on the same page.
> 
> These are the kind of batteries I work with, and these are small ones.


In that photo I see bus bars connected to the battery cell terminals. There is a terminal plate with cover on each side on the top. No fuses hanging off the battery posts are visible. It looks like a proper installation. Thanks for the support.

BTW, it appears to be similar in size to batteries which I worked with for many years.


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## Sunking (Aug 10, 2009)

major said:


> In that photo I see bus bars connected to the battery cell terminals. There is a terminal plate with cover on each side on the top. No fuses hanging off the battery posts are visible. It looks like a proper installation.


You are correct, there are no fuses in this particular installation. This is a telecom install at a cellular tower. This particular telephone company does not require fused battery links. Those that do, I provide Fuses like this one mounted onto the Term Plates, then attach the cables to the Fuse.


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## major (Apr 4, 2008)

Sunking said:


> You are correct, there are no fuses in this particular installation. This is a telecom install at a cellular tower. This particular telephone company does not require fused battery links. Those that do, I provide Fuses like this one mounted onto the Term Plates, then attach the cables to the Fuse.


So you mount the fuse to the terminal plate, not the battery post. What is the point? How is that different from Ziggy's install shown in post #7?



Sunking said:


> but I do not like the holders designed for then as they require to be mounted away from the battery post.


You start this thread asking about fuses mounted to battery posts like those Blue Sea blocks. I tell you it is a bad idea to start with and nobody else in their right mind uses the method on EVs and you start telling me we're not fused at the source and then show this unrelated installation. You don't tell us what the application is and this is an EV forum, so it is not far fetched we assume it is an EV. I have no idea what you're talking about and why you want to use a 58V rated fuse let alone a 32V fuse on a battery post in an EV


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## Sunking (Aug 10, 2009)

major said:


> So you mount the fuse to the terminal plate, not the battery post. What is the point?


 Because the battery post is only a single hole mechanical connection that does not have the strength to support the fuse or cable lug terminations. In order to terminate the pair of 2/0 cables requires a term plate. The cable lugs are 2-hole 1/2 inch hardware. 



major said:


> You start this thread asking about fuses mounted to battery posts like those Blue Sea blocks. I tell you it is a bad idea to start with and nobody else in their right mind uses the method on EVs


I never said I wanted to use it on an EV, you assumed that. I am simply looking for other options on 12, 24, and 48 volt solar applications and thought I might get some ideas here. So far I have not found anything better than a MRBF or AGM for my application. I thought this might be a good place to ask. Is it not?

What I do not care for about Ziggy illustration is the unprotected length of pig tail cable between the battery post and fuse holder. If he is comfortable with it and allows him to sleep at night, OK. But where is the second fuse for the opposite polarity if the system is not grounded? One fuse will not work on a floating system.


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## major (Apr 4, 2008)

Sunking said:


> Because the battery post is only a single hole mechanical connection that does not have the strength to support the fuse or cable lug terminations.


Bingo. That is what I have been saying.



Sunking said:


> I never said I wanted to use it on an EV, you assumed that.


This is an EV forum. If your thread is unrelated to EVs, at least have the courtesy to warn us by using the words "off-topic" or "non-EV related" in your thread title, please.


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## Sunking (Aug 10, 2009)

major said:


> This is an EV forum. If your thread is unrelated to EVs, at least have the courtesy to warn us by using the words "off-topic" or "non-EV related" in your thread title, please.


OK point taken.


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## major (Apr 4, 2008)

major said:


> How can you get a tight clamp on the high current lug contact without compressing an insulator? And that will fail, eventually.
> 
> 
> Sunking said:
> ...


It sure looks like that fiber washer is compressed, not to mention the plastic body of the fuse itself.












Image from: http://www.bluesea.com/articles/640

edit: 2nd attachment from: http://www.docstoc.com/docs/33529882/MARINE-RATED-BATTERY-FUSE-(MRBF)-BAR-104


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## PStechPaul (May 1, 2012)

I'd be worried about getting a really tight connection with the fiber isolation washer, especially in the automotive environment with vibration and thermal cycling and contaminants (water, salt, dirt, etc). Also, with the high voltage of most battery packs, there may not be enough creep distance between the stud and the fuse to avoid arcing and insulation failure. I agree that bolting one end of a lug terminal fuse to the battery terminal and connecting a cable to the other end without support is not good and could result in flexing of the fuse body and degradation or breakage. It should be possible to use an insulated standoff for the other end of the fuse.








http://www.glastic.com/en/products/glastic-electrical-products/electrical-standoff-insulators.html


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## bjcouche (May 17, 2013)

OK, now that we know this is NOT an EV application, I'll explain what we do and why we do it, or rather what the OEM's do and the DIYers SHOULD do. I understand your reasoning for placing a fuse as close to the battery terminal as absolutely possible, it's a good goal. I have never seen those marine fuses before, real neat. How much torque can you torque the bolt to before the insulator portion of the fuse cracks? How much heat does the fuse generate and heat up the battery through the terminal?
OK, what the OEM's do is to NEVER bond the battery pack to the frame. They usually have a series fuse not on the + and - legs of the battery, but installed about midway through the string. If you install fuses with pigtails between the + terminal and the rest of the vehicle, even if the fuse is located INSIDE the battery box, then there is still a short length of cable that is unprotected. Placing the fuse in the center of the pack protects the pigtails coming off the + and - terminals going to the connector that leaves the battery pack. If there is a connection or either + or - to chassis, then the battery management system senses this as a ground leakage and turns off the power contactors and no power leaves the battery. It doesn't need fuse blowing current to sense a ground fault, just milliamps. These internal power contactors are INSIDE the battery box that turn off all power leaving the battery when the vehicle is turned off. NO HV power is ever allowed to be on with the ignition off. There is ALSO a manual disconnect required to disconnect all power from the battery. Normally I have seen this also in the center of the battery string. Sometimes the disconnect is integrated into the fuse as a removable fuse disconnect.
My suggestions to you is to consider placing your fusing in the middle of the pack and inside the battery box. Also, never exceed the voltage rating of a fuse, and consider the fuse blowing curve for the application. Those automotive fuses allow tremendously large currents to flow before blowing and are not considered "fast blow" or "current limiting" fuses. The round littelfuses that you showed are good fuses, although expensive. The EV group often uses the Shawmut A30Pxxx or A50Pxxx fuses as they are DC rated, current limiting, semiconductor type, easily sourced and almost affordable.
Brian


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## TexasCotton (Sep 18, 2008)

Sunking said:


> You do not compress the insulator, all the mechanical strain is on the MRBF fuse which is made for it. I would send you one to look at but they are expensive.
> 
> I am asking what you guys use at the source. I have my answer. You do not use anything at the source. YOu take your chances. Got it loud and clear.


Sunking you making friends again.


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## Sunking (Aug 10, 2009)

bjcouche said:


> I have never seen those marine fuses before, real neat. How much torque can you torque the bolt to before the insulator portion of the fuse cracks?


50 to 70 inch pounds, same as you would apply to battery terminal post type AP



bjcouche said:


> How much heat does the fuse generate and heat up the battery through the terminal?


I do not know, no data published I am aware of



bjcouche said:


> OK, what the OEM's do is to NEVER bond the battery pack to the frame.


 Yes I know and understand why.



bjcouche said:


> They usually have a series fuse not on the + and - legs of the battery, but installed about midway through the string.


That I did not know, I assumed they floated the supply, and fused both polarities or GFD to provide over current protection.



bjcouche said:


> If you install fuses with pigtails between the + terminal and the rest of the vehicle, even if the fuse is located INSIDE the battery box, then there is still a short length of cable that is unprotected. Placing the fuse in the center of the pack protects the pigtails coming off the + and - terminals going to the connector that leaves the battery pack. If there is a connection or either + or - to chassis, then the battery management system senses this as a ground leakage and turns off the power contactors and no power leaves the battery. It doesn't need fuse blowing current to sense a ground fault, just milliamps. These internal power contactors are INSIDE the battery box that turn off all power leaving the battery when the vehicle is turned off. NO HV power is ever allowed to be on with the ignition off.


 I knew they had to provide over current protection somehow, but until your post no one stated how it was done. So in effect they make it a Bipolar Supply with Ground Fault Detection and Protection is what you are saying? That I understand and is exactly how ungrounded 3-phase Delta AC power operates . 



bjcouche said:


> My suggestions to you is to consider placing your fusing in the middle of the pack and inside the battery box. Also, never exceed the voltage rating of a fuse, and consider the fuse blowing curve for the application.


Thanks for the suggestion but unfortunately it would not work out in off-grid solar because just about all the equipment made for solar is designed for the NEGATIVE Battery Polarity to be grounded. The manufactures bond the negative polarity to the chassis, and a few, very few float the battery polarities to allow either a floating system, or a neg or positive ground. Only those very few who float the equipment could that be possible. 

Brian *thank you* for taking the time for the explanations. You clearly understood my questions and answered my questions fully. I now clearly understand waht is going on with EV over current protection. I knew it had to be done.


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## bjcouche (May 17, 2013)

An EV battery pack isn't really like a bipolar power supply because there is no center tap. Yes the fuse is in the middle, but there is no output connection there. The fuse is inside the battery pack and only the + and - connections leave the battery. The type of ground fault detection isn't like GFCI breakers you find in the home. Those sense a difference between the incoming and outgoing current with a current sensor around both polarities. This system only senses a ground fault if there is current flowing. An EV battery pack the BMS (battery management system) actively checks to ensure the battery pack is floating from the chassis. 
One way is to place a high resistance, say 10M ohms from + to chassis and measure the voltages from + to chassis and - to chassis. With the resisitor connected + to chassis, the voltage - to chassis should read near pack voltage. Then the BMS would do the opposite, connect the resistor - to chassis and read the voltage + to chassis. If during these tests the system doesn't read full pack voltage, that means there is a current leakage path to chassis somewhere, either inside the pack or external. The BMS actively does these tests continuously. If a fault is found it either issues some type of warning or turns off the pack power contactors and shuts off power external to the pack.

You could in theory, touch any single HV connection anywhere inside the battery and not receive a shock because there is no path to chassis.

Note that this is how the OEM's do it, those that have to follow SAE rules, laws, and such. DIYers usually don't do any of this. They usually just float the pack and have 1 fuse on the + side. They usually find they have a ground leakage problem when they touch a battery terminal.

Factories that use a floating delta, or more likely a floating Y with voltage sensing on the Xo to sense a ground fault do so for downtime reasons. There is usually enough current, phase to ground to electrocute you. In an EV it's done for personal safety.


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## Sunking (Aug 10, 2009)

Brian what you are describing is a high impedance ground fault detection which I understand. Here is a diagram from a very high tech device from the early 1900's, which set off both visual and audible alarms to alert plant maintenance engineers of impeding doom. Audio circuit alarm not shown for simplification.


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## PStechPaul (May 1, 2012)

That circuit reminds me of a ground integrity circuit I designed for high current circuit breaker test sets, which typically connect to two phases of a 480 VAC supply. I connected two 100k power resistors to a common point, and from that point to the chassis of the test set I connected a neon-lamp SSR, such that it had to be energized before the main power to the test set could be turned on (I used an undervoltage trip device on the 400A main breaker). But it failed to operate correctly for certain configurations, particularly floating three phase delta, where there is no neutral. So, instead, we used a method similar to that of other manufacturers, where an "isolated ground" jack was provided, with the idea that it should be separately connected to a known good earth ground to which the chassis was to be connected. It used a low voltage and a moderate current to assess ground integrity before allowing the main power to be turned on. But of course most customers just installed a jumper between the two ground connections which defeated the purpose.

I have been unpleasantly surprised when doing a field calibration on one of these test sets, where my instrumentation was showing a lot of AC noise and it was impossible to get a good reading. Then as I was leaning on the chassis and fiddling with the ground connection on a scope, I got an uncomfortable tingle. When I pulled the test set away from the wall and looked at the input connections, there was no ground connection! Yikes! 

It is difficult to design a GFCI circuit to provide human shock protection for high power devices such as these, and it is probably similarly so for EVs that have potentials of several hundred volts and normal currents of hundreds (or thousands) of amperes. A CT with both power cables running through it will pick up common mode currents, but a 500/5 amp CT will not accurately provide an indication of the 20-50 mA current that is considered lethal. And it may be even more difficult for DC, because of offset errors of Hall effect devices.

Thus, it is best not to rely on the main DC power to be floating with a high enough impedance to ground to limit current to safe levels. Bottom line, "Don't touch anything", and always keep one hand in your pocket.


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## Sunking (Aug 10, 2009)

PStechPaul said:


> That circuit reminds me of a ground integrity circuit I designed for high current circuit breaker test sets, which typically connect to two phases of a 480 VAC supply.


Surprisingly the circuit is still in use today, and is effective even with 3-phase 3 wire Delta service. Of course it has been modernized with more Bells, Whistles, and controls, but the basic circuit is stil used. Walk into about any electrical substation and on one of the control panels and you will see 3 dimly lit incandescent bulb glowing. If you see two light glowing bright and on edark you know immediately you have a huge very dangerous problem. It works for both AC and DC systems.


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