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Old 10-04-2015, 06:03   #1
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Proper Stackup

This question is a little strange but might be relevant for others as well.

I've been doing some serious rewiring (and reading in order to get it right). In my reading I've come across several references to the fact that improper stackup causes heating and can even cause boat fires. I'm wondering if anyone can explain why this is the case? Just increased resistance in a high current circuit?

I think I've "always" understood that the proper order for stacking (for something like a bussbar or battery terminal) is: cable ring terminal, flat washer, lock washer, nut. But that raises a few questions. When you have more than one cable on the same terminal, how do you stack them? The crimped ring terminals are not symmetrical, i.e., one side is "higher" because the crimp is asymmetrical. I assume that you just have to be sure that they are flat and in good, complete contact when bolted down.

How many cables or wires can be located on one stud (maximum)? I've read three and that makes sense to me but I wonder if anyone has a comment.

I've found a couple of places where the flat washer is missing in the stackup. I guess I'll just buy a few and put them in. I'm uncomfortable having the lock washer pressing down directly on the cable or fuse ring. Since the lower AWG cables are going to things like copper bussbars or fuses, I assume these should be brass washers. No point in having too many different metals.

I've also got a boatload of terminal strips connecting wires (cables) for distributing power to all sorts of equipment. Wire sizes ranging from about 12 to 18 AWG. These don't seem to be tinned copper with brass screws but they are all working fine. They don't have any washers, flat or lock. But they are all tight...some are VERY tight so I assume that these just rely on the screw head for contact and the thread for tightness.

On a slightly different note. I've got some "conducting" grease that ham radio guys use on antenna connections, etc to prevent corrosion where there is weather. I've been using it judiciously on some of the large connections like battery cables and big fuses.

I hope there are some wiring gurus who'll comment.

Thanks
Bill
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Old 10-04-2015, 08:27   #2
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Re: Proper Stackup

If you stack with washers the washers in some case don't transfer power so the electrical connection is actually only at the bolt. I forget which washers are worst for this. Stainless? Best practice as I understand is never put washers between stacked wires and add a bus block when possible for multiple conections.

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Old 10-04-2015, 08:57   #3
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Re: Proper Stackup

Yes, here are photos of a stainless washer causing a battery terminal to melt.

His hall of fail is also fun to read. Maybe we need a thread like that here?
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Old 10-04-2015, 10:05   #4
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Re: Proper Stackup

Hmmm. I should have found the MaineSail article. So, I'm thinking that the general rule is to keep the connectors touching, i.e., no washers between them. So on a battery or buss bar the ring connector is on the bottom to make best contact. On something like an ANL fuse, the ring connector and the fuse connection should touch. Flat washers are kind of an option but a lock washer should be used whenever it will fit and if it won't fit, a nylok. He says AYBC standards allow 4 ring connectors...that sounds like a lot to me. And they should be stacked in order of ampacity Highest to Lowest. That all makes sense but it's definitely worth remembering.

Bill
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Old 10-04-2015, 10:46   #5
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Re: Proper Stackup

Bill E,

You got it right.

I can't tell you how many incorrectly-stacked connections I've seen, often because a stainless steel washer is inserted between the two conducting sufaces.

Stainless is a poor conductor of DC current. If you're using flat or lock washers, install these immediately below the nut.

Also, sometimes turning one ring terminal upside down makes for a neater compact stack.

Bill T
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Old 10-04-2015, 10:55   #6
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Re: Proper Stackup

Its not the stacking that is a hazard. It doesnt matter what connection you choose the basic principles always apply. Size all elements appropriately. Choose the correct materials. Assemble correctly. Finally test when finished. Voltage drop and resistance using your multimeter. For high current runs check temp under load also. IR hand held temp sensors make this easy today.

Electrical fires are caused by temperature of a component exceeding a flammability threshold. This threshold may be from poor assembly, latent defects, lack of fusing, undersized components, corrosion, gradual metalurgical degradation, or ignition of adjacent flammable items.

The problem with stackup is you cant see distortion in the stack which may lead to increased resistance. The ideal stack is one. Another rule of thumb is not more than 4. Also stack similar size / thickness. The stack should be well supported and you want to maximise the surface area. Avoid washers, connectors and tightening that results in distortion. Also watch out for corrosion from dissimilar materials.

I also like to stack in logical groupings. Labelling and fault finding become more intuitive.

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Old 10-04-2015, 11:13   #7
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Re: Proper Stackup

One consideration: Instead of stacking, consider using Power Posts with multiple screw attachments where feasible.
I've always failed to see what it matters what the flat washer is made of, all the eye connectors below it should be in contact with one another and the washer is just to keep them intimate. Heck it could be non conductive. In theory the electricity shouldn't even need to flow thru the flat washer. What am I missing?
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Old 10-04-2015, 12:33   #8
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Re: Proper Stackup

Do you guys have an opinion on DIN rail mounted terminal blocks for large wires?

Some of them are specced for up to 4/0 wire and 250 amps. I've used DIN terminal blocks for smaller wires, and like how compact and easy they are to use.

I'm so used to seeing large battery cables using good old fashioned solid crimps with lugs/ring terminals on boats. However, my reading of the ABYC standards say those kinds of connections are conforming as long as the wire is held steady, as long as the terminal is the kind where a plate mashes the wire instead of the screw directly.

By the way, I also try to have only one terminal per bolt. It makes it a whole lot easier to troubleshoot. Ancor or Blue Sea make little solid bus bars that are perfect for jumping between the master switch to the bus bars, to the individual fuse blocks, to keep it all relatively compact. Photo attached.
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Old 10-04-2015, 18:29   #9
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Re: Proper Stackup

I have used din rail terminals in industrial control panels. There are a lot of useful relays and fuse holders, etc available. Wonder what ABYC thinks.

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Old 10-04-2015, 21:59   #10
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Re: Proper Stackup

ABYC says 4 per post max.

put the larger cables on the bottom. only use a washer on the top with the nut. not inbetween and not underneath the lugs. some lugs with some buses you can put 2 on top of each other with the lugs facing opposite. otherwise the only way to fit more then 1 or 2 is to have the wires facing different directions off the post.


the din rail things are not good for a boat. everything should be closed faced lugs with heat shrink. not screwed in lose wires that will corrode.
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Old 11-04-2015, 14:19   #11
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Re: Proper Stackup

Quote:
Originally Posted by Bill_E View Post
When you have more than one cable on the same terminal, how do you stack them? The crimped ring terminals are not symmetrical, i.e., one side is "higher" because the crimp is asymmetrical
. Turn every other one upside down. You may also have to angle them away from each other.

Quote:
How many cables or wires can be located on one stud (maximum)?
The ABYC allows four.
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Old 13-04-2015, 15:39   #12
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Re: Proper Stackup

Check for problems: discharge the battery bank to your lower limit and with your maximum recharge capability (alternator or shore power) use an IR temp sensor on the terminals to check for excessive heat or resistance in every connection. Look for high temps and/or differences in temps from one terminal to the next - this should make it obvious where the problems are.
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