Small Busbar connections.

[daveNZ]

Some Blueseas Busbars have a #10-32 screw terminal fixing.
Apart from the usual limits on maximum for the bar etc., what is a reasonable limit for this one connection. I can’t find any specs. for this.

i.e. a #10 screw is about 5mm where I am, and the nearest lugs are 6 mm. I can get a 6mm wire /6mm hole lug, and, depending on temp. rating of insulation, a 6mm wire has an ampacity of 30 to 60 Amps.

Is it reasonable to use these screws for a 45 Amp connection? The screw just seems a bit lightweight in terms of compression a battery lug or wire crimp style terminal???

[coopec43]

Can't you get some idea from a link like this? (Why do you use "Blue Seas" busbars?)

https://www.ebay.com.au/sch/i.html?_...sbars&_sacat=0

[Manateeman]

Why not just go up in sizes. Not just the recommended size. What all the tables do not account for is corrosion. Are you somehow limited?
If that little voice in your head says “ this looks a little small” why not just increase everything.

[Shrew]

What is the model and specs for the busbar??

A Blue Sea Systems 2105 Maxibus 12 X 10-32 Common Busbar is rated at 250amp.

https://www.amazon.com/Blue-Sea-Syst...38974340&psc=1

It will depend on the model. There are 8x32 rated at either 100 or 150 amp. The screw size alone will not tell us the max capacity of the bus bar.

[Shrew]

As for the terminals themselves. I've never seen a #10 sized lug. I've only ever seen this in a ring terminal. A #10 ring terminal usually only comes in 10-12 gauge wire. at 8 gauge about the only thing you could get are lugs and I think it would be crowded to use a lug on a bus bar with #10 screws.

[Jammer]

The screw doesn't conduct current to any meaningful degree. It's just there to clamp the wire termination to the busbar.

Ordinarily #10 screws are used with ring terminals with wire as large as 10 gauge.


Usually 5/16" or 3/8" fasteners are used for busbar connections for larger wire.


I myself am a fan of using the two-hole lugs for larger connections to busbars though they are rarely used in marine applications. The advantage is that the lug won't twist on the busbar and work itself loose.

[Manateeman]

Two hole heavy duty lugs. That’s somebody who knows how to do it right.
Blue Sea System buss bars are a lot heavier than BEP and rated in a different ( real) way. You can always build your own as the copper industry has all the info online and the raw material is easy to find on eBay.
We have American hydraulic crimpers which help.
The manatee crew.

[daveNZ]

Thanks for the replies….
- I use Blueseas as sold nearby, and I trust their rating over BEP
- I can go up in size, the question is just ‘how much current can I put through this screw connector. I have 45A requirement and running out of larger connections, next size up Busbar is another $100. So trying to see if the Busbar I have will work.
- I’m quite aware the screw is not an amperage factor, but will it clamp hard enough for a good connection that ‘can’ carry 45 A?
- my sizing theory is this…. #10 screw equates to about AWG 10, or 5mm, and I can’t find 5mm lugs, but I can find 6mm. I have 6mm lugs that are 6x6 so take 6mm wire. So I can use 6mm wire with this #10 screw, but will the screw hold tight enough for a good connection? Simple! That was the original question. Nothing to do with overall capacity of the Busbar.
- best answer probably is, if it looks under sized, it might well be!
Cheers,
Dave
-

[CharlieJ]

@daveNZ: #8

So I can use 6mm wire with this #10 screw, but will the screw hold tight enough for a good connection? Simple!

Simple question...simple answer: Yes.

[coopec43]

Originally Posted by Manateeman

Why not just go up in sizes. Not just the recommended size. What all the tables do not account for is corrosion. Are you somehow limited?
If that little voice in your head says “ this looks a little small” why not just increase everything.

Absolutely! (Not a big deal!)

When building my yacht I've used heavy duty bus bars but attached light loads to the bus bar as well.

When I used post type busbars and I considered it sensible I've used copper washers to increase the area of contact

[deblen]

Mostly my opinion,but with substantial real life marine electrical experience & the following ampacity link:
Yellow crimp ring terminal physical capacity is #10-#12 AWGauge wire.
The ampacity of #10 wire is 30-35A @ 100% load in normal Rec. boat lengths.
Recommended safe continuous load is 80% of above. .8x35 =28Amps max cont.

Therefore,IMHO,45Amps could overload a Yellow crimp terminal?? regardless of what screw/bolt size is holding it down. Yellow crimp ring terminals are available in up to 1/2" bolt size but I wouldn't use a yellow crimp for more than 20A personally. Cheers/Len


https://www.batteryequivalents.com/1...re-handle.html

[RaymondR]

The short bit between the crimp and ring sections always look too small to me.

[daveNZ]

Totally agree with you Len, and Raymond, so I’m using battery cable lugs. Local Blueseas dealer has a hex brand, 5mm hole, up to 10mm wire! So in my mind the limiting factor is still, what amperage exceeds the torque capability of a #10 screw !?
Maybe it’s a function of torque? My Busbar spec is :
The 5/16” stud spec is 120in-lbs
The #10-32 screw spec is 18in-lbs

A quick google shows a maze of torque info for industrial electrical work. I wonder if somewhere there is a spec of:
50A requires torque of in-lbs between similar metals etc. ???

Getting slightly esoteric here but…it would be convenient to find a guide.

[rgleason]

Why not tap for 5/16"

[Jammer]

Dave,


I don't think you'll find a guide. I've never seen a table or handbook of fastener sizes and torque ranges vs. amps.


Engineering wise, the real question is whether the assembly as a whole overheats. The terminals, the wire, the busbar, all conduct heat just as they do electricity. Localized heating in, say, the ring terminal or the lug, is not a problem as long as it does not exceed the ability of adjoining materials to dissipate the heat.


The very conservative USA residential wiring standards based on 1905-era rubber insulation allowed 30a in 10 gauge wire. ABYC ratings match this with 75* F wire. ABYC ratings with modern 90*F wire are 55 amps; 45 amps in an engine space.


With a larger lug and the smaller fastener my main concern would be the effect of twisting forces that could loosen the fastener. I will say that in USA building wiring it is not uncommon for a 10-24 fastener to "land" a ground lug for #8 wire. 10-32 fasteners are stronger than 10-24 fasteners.


You be the judge.