Split nut connection

Is the type of connection wrong? 2- 200 AMP Square D panels side by side. Wire coming out the right panel and connecting to the wire above the panel of the left. I have never seen a connection like this, but I do learn something new every day.

It is hard to tell from the pictures, but I am guessing that you are looking at the ground conductor for a system that uses 2-200 amp panels fed from two sets of lugs in the meter base to produce a 400 A service. In that case the ground conductor would connect to a single ground rod. Did you see one? Very common for larger homes around here.

Ground rod in ground and ground on water pipe.


There is however a violation in that picture set. Each two hundred ampere panel is supplied by 4/0 Al conductors. Since neither of those could possibly be the “the main power feeder to a dwelling unit” the use of conductors sized in accordance with 310.15(B)(6) is a violation. The diversity on which 310.15(B)(6) is predicated is not assured when the load is split across two sets of service entry conductors. The Service Entry Conductors should be sized in accordance with 310.15(B) and thus taken directly from table Table 310.16. The net effect of that is when the 400 ampere load for one dwelling is split across two sets of Service Entry Conductors each set must be capable of carrying a full two hundred amperes which gives you a minimum conductor size in Al of 250 Kcmills or one size larger then is commonly available in SEC cable.

Tom Horne

I’m not trying to nit pick but the term of art is a “split bolt” connector. Calling it a split nut won’t help your credibility with the electrician that gets called in. That method of running the Grounding Electrode Conductor is specifically permitted by the NEC in

“250.64 Grounding Electrode Conductor Installation.
Grounding electrode conductors shall be installed as specified in 250.64(A) through (F).
(D) Grounding Electrode Conductor Taps. Where a service consists of more than a single enclosure as permitted in 230.40, Exception No. 2, it shall be permitted to connect taps to the grounding electrode conductor. Each such tap conductor shall extend to the inside of each such enclosure. The grounding electrode conductor shall be sized in accordance with 250.66, but the tap conductors shall be permitted to be sized in accordance with the grounding electrode conductors specified in 250.66 for the largest conductor serving the respective enclosures. The tap conductors shall be connected to the grounding electrode conductor in such a manner that the grounding electrode conductor remains without a splice.”

If you read that with great care and patience you will see it specifically covers the situation in your second photograph providing that the conductor and the tap are sized correctly.

Tom Horne


I have been squaking about this one for years…and agree with this application as you have layed out. However, what if the calculated load does not exceed 180A on each. Would you then have a problem with this application?

In that allowance for where you have a grounding electrode conductor that is continuous from the electrode under the panels in question. The NEC allows for the grounding electrode conductor taps to extend into each panel. If the grounding electrode conductor runs all the way into one of the panels…would you consider it a grounding electrode conductor tap that extends into the panel and would this meet the intent of the allowance.

Typically we would see lets say a 4 AWG CU from lets say a UFER run to the location under the panels. Then lets say you have (2) 200A panels which the allowance of 250.64(D) allows grounding electrode conductor taps to tap onto the unspliced 4AWG CU with 6 AWG CU and extend into both panel enclosures as permitted in the NEC…in the application shown the grounding electrode conductor runs continuous into panel (1) and then panel two taps onto the (1)…do you feel this meets the intent of the allowance?

lol…Split Nut…now thats just plain funny…Sorry Buck…:wink: