Stranded MLO double lugging?

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Andy Delle

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Los Angeles CA
Is stranded double lugging on a MLO panel allowable. Meaning a tap off the feeders? We are talking #4 here and will compress nicely in the lugs.

It just seem this would be far more reliable than a taped up split bolt connection
 
Andy Delle said:
Is stranded double lugging on a MLO panel allowable. Meaning a tap off the feeders? We are talking #4 here and will compress nicely in the lugs.

It just seem this would be far more reliable than a taped up split bolt connection
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Yes usually not allowed, but what are you trying to do exactly? I would probably just add a breaker. Another option is to replace the lugs with two port lugs, although this is not always doable on small "loadcenter" type panelboards, and some would call it a 110.3 violation.
 
Commercial style panelboards (NQOD or similar) usually have options for sub-feed lugs (basically 2 sets of lugs on the breaker) or feed through lugs. Those are basically a second set of lugs on the bottom of the buss (assuming your panel is top fed).
 
wwhitney said:
As a general matter, how does one tells if it is "doable" or not?

Thanks, Wayne
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Well I dont think there is a simple answer. Mechanically, I think it would difficult to do in a smaller loadcenter. stacked/step style lugs dont seem to be available in small sizes, and the side by side ones usually dont fit. Putting lugs on the other end of the buss as a "feed thru" is of course usually not possible in loadcenters as there are no provisions for the mounting. Code wise, I think it is always a potential 110.3 unless you use lugs approved or supplied by the manufacturer. I think in practice, as equipment get larger, it generally becomes more and more accepted that one can move, add, and change lugs around. I personally do not hesitate to change lugs if it suits me. I feel that is well within my skill set as an experienced licensed professional, and I have never had problems. In a few extreme cases, such as when I needed to keep the metering section of a switchboard and throw out the rest, I have sought AHJ approval first.
 
wwhitney said:
As a general matter, how does one tells if it is "doable" or not?

Thanks, Wayne
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IF, and only if, the lugs themselves, or an instruction sheet for the panel, SPECIFICALLY states that you can put more than one conductor per terminal. Without EXPLICIT listing and labeling as such, you cannot. If not, then the other options may be viable: feed-through lugs on the other end of the bus, double lugs as an APPROVED AND LISTED accessory for that specific panel, or adding a gutter above it with a Power Distribution Block of some sort in it. It’s unlikely that you would have room to legally add a PDB in the existing can, you need to have legal wire bending space clearances.
 
Why not use a separate breaker for this?

As others have mentioned, unless the existing lugs are rated for two conductors, you cant tap off the mains with #4 (or any other size) wire.
 
Jraef said:
double lugs as an APPROVED AND LISTED accessory for that specific panel
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So you're of the opinion that even if there is sufficient wire bending space and clearance between live parts, one can't generically swap out single lugs for double lugs or add a second set of lugs? For example, the automatic transfer switch below comes with a relay that has single lugs on one side and two sets of lugs on the other. It certainly looks like there is room for two sets of lugs on both sides:

TeslaPowerwallBackupGatewayRelay.jpg

But if the manufacturer hasn't tested and listed a configuration that include two sets of lugs on both sides, then it would be a 110.3(B) violation to add a second set of lugs on the top side? 110.3(B) doesn't follow the usual NEC philosophy of "if it isn't prohibited, it is allowed"?

Jraef said:
or adding a gutter above it with a Power Distribution Block of some sort in it.
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If there's adequate space in the cabinet, any issue with just using Polaris-style insulated mechanical connectors? That makes me wonder whether a product exists that is an insulated mechanical connector with an uninsulated pin emerging from it to go into a set-screw style mechanical lug. Like a cross between an insulated mechanical connector and a pin reducer.

Cheers, Wayne
 
I don't know enough about the listing and approval process to say if there is sufficient detail in the wording to address whether we are allowed to change lugs. We are allowed to punch holes in cabinets, isn't that "modifying" the equipment? Some anecdotal evidence for allowing us to:

The class 320 sockets we get around here do not come with lugs

Recently, a 3000 amp switchboard we installed had no lugs on the ground bar

We have lots of listed lugs and nema standard bolt patterns

The nec allows us to bolt lugs to cabinets for grounding connections
 
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