BIGRED

I know it is not legal to have two conductors under one lug of a 100-a main breaker (one going to a sub-panel) but where can I find this in the code book or any where else?

brian john

The information you require is on the circuit breaker, listing the number of conductors allowed per connector.

electricista

Article 408.41 prohibits 2 wires termination for grounded conductors. I don't know any rule that prohibits the ungrounded conductors from having 2 wires as long as the termination is rated for that type of install. I don't know of any main lugs that allow multiple wires under a terminal/lug but I haven't checked those lately.

__________________
Alice

"I complained because I had no shoes until I saw a man who had no feet."

jfwfmt

The other book you need in addition to the NEC is the UL White Book, available on line at WWW.UL.COM. Molded case circuit breakers are listed under DIVQ. This references AALZ which is the base instructions for almost everything. AALZ states:

"Terminals — Product terminals, including wire connectors and terminal
screws, are acceptable for connection of only one conductor, unless there
is marking or a wiring diagram indicating the number of conductors
which may be connected."

/s/ Jim WIlliams

user5941

If you look at the lug and it is round then only one cunductor can be landed but if it is oblong then two conductors are allowed

kbsparky

The rule you are seeking is found in 110.3(B)

So, you look for the data associated with the lugs in your panel or main breaker, and there you will find the number and size of conductors acceptable for use with that device.

electricista

I still think that it must be stated on the panel that 2 conductors are permitted.

Are you saying that all listed 2 conductor terminals would have oblong holes?
Never heard that..

__________________
Alice

"I complained because I had no shoes until I saw a man who had no feet."

william1978

I haven't seen a lug that has oblong or egged holes not be listed for two wires.

wirenut1110

Unless the wire is 1/0 or larger, it wouldn't really matter whether the lug can take 2 wires anyway would it?
100 amps doesn't seem like it would be this size wire. So this parallel set up is illegal anyway.
Am I reading this right?

__________________
Jim

brian john

And the answer is LOOK ON THE CIRCUIT BREAKER FOR INSTRUCTIONS.

waco

I don't believe there is any way to make the connection legal. However, you could feed the sub with a two pole breaker in a normal position. You can just about always find room in the panel since some branch circuit breakers in there are always underloaded.

redbeard43

I come accross many lugs that are oblong and the actual mechanical lug says for example
1-300kcmil or 2- 3/0

The lug must be marked in order for it to be legal. I have also seen main breaker with double lug kits from the factory, for instance 2 A phase lugs-2 B phase Lugs and so on. Single lugs should be only single cable in my opinion. The panel should have a sticker in it that says what the breaker will accomodate either 1 or 2 wires. I agree with Waco, if possible set a sub breaker which most panels will take up to 125a with out a mounting kit.

__________________
You have the ring, and I see that your schwarz is as big as mine.May the schwartz be with you!

brian john

But fortunately you are not UL (or another listing agency unless I missed something). The listing agency and the manufacture get's to make that decision.

Single lugs that were designed for two conducors work for the application, are designed for the application, and are approved for the application and I see no issue.

Welcome to the forum.

redbeard43

[quote=brian john;65983]But fortunately you are not UL (or another listing agency unless I missed something). The listing agency and the manufacture get's to make that decision.quote]

Correct, but as I mentioned b4 "The lug must be marked in order for it to be legal". I have came across many double lug situations and most of the time there is a loose connection from over the years. Tork ratings should always be followed according to the UL sticker of mftr requirement. Over tightening can strip out the bolt or maybe the bolt will not seet right therefore letting the copper to expand and contract possible causing the bolt to loosen, in my personal opion others may see it another way.

__________________
You have the ring, and I see that your schwarz is as big as mine.May the schwartz be with you!

MDShunk

In the case of many older breakers, you have to physically remove the entire breaker to find the little sticker or mold markings that indicate the size and number of conductors each lug is rated for. Sort of a bummer.

__________________

brian john

We do 100's of infrared scans a year (full buildings) commercial, industrial, hospitals, stores and data centers. We see 1000's of connections, to my knowledge we see no more percentage of failures with connectors with 2 conductors that single connectors.

The number one failure item is the Mac Adapt type connector, generally at the connector to conductor.

MDShunk

Do they even still sell Mac Adapts?

__________________

brian john

A quick web search came up with nothing, but I am sure there is some incarnation of this connector out there somewhere.

I think the issue was the use of the wrong compression tool?

MDShunk

I think Burndy makes a similar connector. They were to adapt aluminum to copper only terminals, right?

__________________

KayJay

It sounds like it could be the OP doesn’t want to make this type of connection so much as he wants to know where in the NEC it is not allowed unless the lug is designed for it.
I think that part was already answered, but…. with the main breaker panel located inside a building, wouldn’t you still most likely have contend with 230.70,A [1] regarding the location of service disconnecting means for service conductors entering a building and any local service conductor length restrictions?
I would think that these pieces of service equipment would have to be located right next to each other for grouping of the disconnects.
If these were taps from a feeder then you could most likely utilize the tap rules in 240.21 to supply a subpanel located somewhere near by.
In the OP's case, I’m not sure why you would need to, but for small 100A wire connections as described you could probably just use split-bolts, parallel jaw clamps, C or H-tap connectors ahead of the wire connections to the main CB terminals spaced so as not to exceed 75% fill for that area of the panel per 312.8. Either that or a piece of trough above the panels and then splice before dropping down into two main CB panels.
Unless it’s for a fire pump or something similar, it seems like it would be much easier to just use a DP CB in the main panel and run a feeder.