How many cables fit on a busbar?

[s/v Jedi]

So here’s me considering to put 16 cables onto a 4-stud busbar.... thoughts?

[Sailmonkey]

If it can be done neatly and within the current carrying ability of the bar, I’m all for it.

[rslifkin]

Originally Posted by Sailmonkey

If it can be done neatly and within the current carrying ability of the bar, I’m all for it.

This. If it all fits and everything is within its current rating, I see no problem with it.

[Manateeman]

Another buss bar or two is not that much money and you can connect them with a nice piece of silicon bronze which you can tin yourself.
Just kinda freaks me out even though there might not be a technical reason not to do this. I just like the idea of “testing” one connection at a time by hand.
Do you have a space or access restriction?
Happy trails to you
Mark and his “are you sure the switch is off “ manatees

[Wotname]

Hmm.... I don't like it!

It would be OK for conductors/terminals that only are carrying small currents but presumably all of these terminations will be carrying large currents.

Your proposed arrangement relies on one nut to provide the necessary torque for four terminals whereas the usual arrangement is one nut for one terminal (two at the max.). One nut loses torque, at least four terminals comprised (possibly more).

Normally the current (from terminal to terminal) is carried between the conductors by the bar itself. With your arrangement, current is potentially carried through six additional terminals.

Normally the current passes though two terminal/bar interfaces. With your arrangement, the current might pass through eight interfaces. Every interface adds potential problems.

If there is simply no other practical solution due to say space considerations, then it would work but IMO it is hardly 'best practice'.

If the only reason is to make it look neat or some such, then I wouldn't do it but each to their own etc.

EDIT: if only four cables are carrying large currents, they should be directly against the busbar. If the other 12 cables are oversized for voltage drop considerations (i.e. carrying small currents), then the proposed arrangement should be OK.

[Sternwake]

I think that much mass, if flowing lots of current for long periods of time, will expand and then contract so much that connections will become loose and more resistive, then heat more, and have the process accelerate Until something gives, if not checked at regular intervals and retightened if required.

I do see regular retightening required, If these cables will regularly see high current as opposed to well oversized for minimal voltage drop, but could certainly be wrong.

I'd also use a grade steel 5 bolt nut and correct size and multiples of washers to ensure all ring terminal flts, are indeed flat and tightly fitting for maximum surface area first, then relocate them on the buss bar's stud and torqued properly, perhaps with some Caig DeOxit Shield applied between each layer.

I keep thinking about Phosphor bronze fasteners secured into a thick wide heavy pure copper bar, properly isolated of course.

I just pulled some Non tinned copper battery interconnects from a 40 year old boat. Looks like there was a copper type of anti seize grease used on them at some point. There were no corrosion issues, just hammer crimps and slightly undersized cabling and not quite universal length for all GC-2 batteries.

Lack of tinning can be mitigated and perhaps pure copper on copper is better than multiple layers of tin stacked between conductors.

[Pete7]

Nick, do you have the space to make your own, say starting with a heavy duty bar of copper? covered with perspex so nothing touches accidently.

Currently (sorry) what happens when you want to remove the middle wire on the bottom, what else gets turned off just to undo that one wire? lights so you are now in darkness, the wife's hair dryer or the anchor alarm? any of those could be dangerous

[Jammer]

Originally Posted by s/v Jedi

So here’s me considering to put 16 cables onto a 4-stud busbar.... thoughts?

It's a bad idea for four reasons:


1) You will have difficulty getting all the wires in place and keeping them there while tightening the bolt


2) You will have to derate the current carrying ability of the components. The bottom terminal in the stack is also carrying the current for the top three connections. The density does not allow for heat dissipation.


3) As noted upthread when it comes time to add another wire or troubleshoot problems with a connection on the bottom of a stack your available choices are poor


4) In practice it is hard to maintain proper torque once you start stacking. I don't know why, maybe it's the elasticity of the stud, maybe it's the tendency of the terminals to turn back and forth, maybe it's the softness of the metal the terminals are made from.



High reliability installations e.g. telecom use busbars with two holes per terminal (better clamping pressure and that way they don't twist loose), and don't stack connections at all, ever. e.g. https://www.totalconnections2009.co....terminals/1057

[mvweebles]

I believe ABYC specifies no more than three wires per connection.

Blue Sea makes an 8 stud bus bar for 3/8" terminals. Not cheap but the right bus bar for the job.

https://www.bluesea.com/products/210...8in-16_Studs__

[Knotical]

I am no expert by any means but I would be concerned with the weight on that single bus bar with all the wires and lugs, weight that is transferred to screws/bolts and the panel.

[Chotu]

I wouldn’t do this. All reasons are already stated above. Just get an additional one.

[skipmac]

Originally Posted by mvweebles

I believe ABYC specifies no more than three wires per connection.

This is my understanding as well and I think for all the reasons mentioned.

[Bycrick]

The bus bar is rated for a specific heat rise. IIRC Blue Sea says 40*C. In a 50*c engine room, that’s 90*c at rated current. Even not running flat out maximum, it’s going to get hot.

Brass is normally around 1/3 or less as conductive as copper. It’s not a good material for a high current connection. Use real copper bus bar material.

There is a specific order for where wires are placed. The idea is to minimize the current through the bus bar itself. Thus, high current wires should be on the same stud. In my case, the inverter can draw more current from the battery than the alternator can provide. So the battery feed and inverter are on the same terminal, with the battery closest to the bar. The alternator is next to it. The highest current connections go towards the middle to reduce path length.

[s/v Jedi]

Well, let’s discuss the issues:

- ABYC # of conductors per stud: ABYC recommends not more than 4 cables per stud, so this setup conforms with ABYC.

- path to terminals stacked on top of one does not go through busbar: that is a pro, not a con. This is exactly like a powerpost single stud which is of unlimited current carrying capacity (terminals/cables determine max. current)

- high current goes through to many contact surfaces: yes, if done without thinking. In practice, one can put the terminal from a battery bank on the stud first, the big charger on top of that, alternator on top of that and now the biggest currents are nit even touching the busbar itself yet.

- connections will go loose: if done right, the nut torqued properly and locked, the stud is in pre-tension and connections should stay tight forever. This is the sturdiest of Blue Sea Systems busbars, with 600A capacity and 3/8” studs.

- undo a cable on the bottom of the stack: I can’t see that happening but if needed, turn everything off and remove the cable; get it done. Inconvenient? Sure but so is every stack of 4/0 cables.

- must de-rate because of stack: not according to ABYC nor any manufacturer. Please provide citation.

- Weight of the total: the weight of the busbar is very substantial in itself. I think the copper bar is 1/2” thick.

Seems that none of the concerns is real and we all feel that it’s a bit much. My biggest issue is that it won’t be possible to expand. The idea of a pair of busbars with a link between them makes things worse, as a 600A rated link doesn’t even fit on a stud (stud not tall enough), so you loose studs for the interconnect.

So for now, I have decided to buy an 8-stud version like someone mentioned for the negative busbar, and use the two 4-stud busbars I have for the 12V and 24V positive busbars.

These two have been used and the tin has worn off a bit and doesn’t look so shiny anymore. I have tinning liquid on the way so will sand and re-tin them.

Things are getting real here... A pallet of solar panels, heaps of cables, Victron gear and now my lithium cells are through customs in Alaska and already left the Fedex hub in Memphis so may arrive tomorrow!

[mvweebles]

I stand corrected.
ABYC (E-11.16.4.1.11) does permit up to 4 conductors on a stud. That said, I doubt it was contemplated to have 4 heavy cables per stud with three similar companions in close proximity.

I would think a skilled electrician would be relieved you've decided to go with an 8 stud arrangement.

Good luck.

Peter