Six Disconnect Rule

[romex jockey]

Then I'm confused....


What is 250.24(B) ex describing here?

Exception No. 1: Where more than one service disconnecting means is
located in an assembly listed for use as service equipment, an unspliced
main bonding jumper shall bond the grounded conductor(s) to the
assembly enclosure.

~RJ~

 

[MasterTheNEC]

Well I guess this is one example that comes to mind.

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[jaggedben]

Greetings Charlie,

Since the rules in 250.28(B) state the following :

(B) Main Bonding Jumper. For a grounded system, an
unspliced main bonding jumper shall be used to connect the
equipment grounding conductor(s) and the service-disconnect
enclosure to the grounded conductor within the enclosure for
each service disconnect in accordance with 250.28.

I would find it hard to not say option 2 was the proper choice. The gutter may be a choice for the GEC connection but not in this case for the MBJ connection.

:thumbsup: This is absolutely the correct answer.

 

[jaggedben]

Then I'm confused....


What is 250.24(B) ex describing here?

~RJ~

That would apply to an MLO panelboard with up to six breakers used as service disconnects. That's not all that uncommon, at least in my area.

It does not apply to charlie's original question because the gutter and disconnects are not a single listed assembly. They are separate listed components assembled on site by the installer.

 

[jaggedben]

FWIW when we install a supply side connected PV system in San Antonio they direct us to use option #1. They require that we install a tap box between the meter and the customer's MDP and move the N-G bond from the MDP to the tap box.

We know from your previous posts that those Texas AHJs you work with lack either the motivation or the ability to conform with the NEC.

 

[MasterTheNEC]

We know from your previous posts that those Texas AHJs you work with lack either the motivation or the ability to conform with the NEC.

And in about 49 other states I can think of on occasion. To error is human.

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[romex jockey]

So you folks are saying installing an MBJ in service rated gutter is a no-no, despite the HB pictures portyaing just that

because the 'listed assembly' addage isn't verifiable universally

well........ what if it is?

~RJ~

 

[MasterTheNEC]

Well I looked at the HB images on PG 179 you referenced and I don't see those as gutters. I see those as assemblies with OCPD inside. Also the one on PG 180 is a SSBJ and not a MBJ so i fail to see where either of those images support your choice of option 1. My graphic i posted a few posts back is a better depiction.

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[romex jockey]

Exhibit 250.12 shows a gutter w/bus bar AND mbj Paul


The HB expanded 'closer look' merely describes the parts as listed for service entrance

Now I realize you may be looking for listed assembly

But that would also mean any resi meter, seu, ,connectors, straps and panelboard w/main would need to be ALL listed as an assembly to meet the main rule w/o the ex



~RJ~

 

[kwired]

So you folks are saying installing an MBJ in service rated gutter is a no-no, despite the HB pictures portyaing just that

because the 'listed assembly' addage isn't verifiable universally

well........ what if it is?

~RJ~

Don't have HB image mentioned readily available to me, but IMO bonding jumper in the gutter is not the "MBJ". The one(s) in service disconnecting means is the MBJ. The gutter must be bonded to the grounded service conductor, via a SSBJ. Said SSBJ can be a lug attached to the gutter and grounded service conductor lands directly on it - similar to how meter sockets are typically bonded.

 

[MasterTheNEC]

Exhibit 250.12 shows a gutter w/bus bar AND mbj Paul


The HB expanded 'closer look' merely describes the parts as listed for service entrance

Now I realize you may be looking for listed assembly

But that would also mean any resi meter, seu, ,connectors, straps and panelboard w/main would need to be ALL listed as an assembly to meet the main rule w/o the ex



~RJ~

Hmmm...I beg to differ.

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[kwired]

Hmmm...I beg to differ.

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

Who is missing what here? I see labels "main bonding jumper" in each service disconnect enclosure and labels "supply side bonding jumper" on all the other bonding jumpers .

From art 100:

Bonding Jumper, Main.
The connection between the grounded circuit conductor and the equipment grounding conductor at the service.

There is no equipment grounding conductor until you are past the service disconnecting means, all the raceways and enclosured ahead of the service disconnecting means don't have an EGC, they are just bonded to the grounded conductor, therefore the MBJ has to be at the service disconnecting means as there is no other point where you transition from grounded conductor to EGC.

 

[MasterTheNEC]

Jockey-

You said in the GUTTER originally....we all agree the MBJ in the disconnects are ok.

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[romex jockey]

yes I said gutter, or perhaps wireway in response to option #1 Paul

and now we've a HB pictoral clearly portraying that

One can purchase a 'power distribution block' (376.56B1),and install it in a service rated gutter via (250.64 F 3)

(3) Bonding jumper(s) from grounding electrode(s) shall be
permitted to be connected to an aluminum or copper
busbar not less than 6 mm thick × 50 mm wide (1∕4 in.
thick × 2 in wide.) and of sufficient length to accommo‐
date the number of terminations necessary for the instal‐
lation.

further, if you've seen MH's vids on this , it's all about a return path to clear a fault.

an MBJ is required , but if multiple MBJ's exist I question the efficacy


~RJ~

 

[MasterTheNEC]

LOL...still doesn't make meet 250.24(B) or the exception but ok...what ever my friend...

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[jaggedben]

So you folks are saying installing an MBJ in service rated gutter is a no-no, despite the HB pictures portyaing just that

...
~RJ~

You are in fact required to bond the gutter to the neutral. But the bond isn't called an MBJ. The MBJ(s) are in the service disconnect enclosures(s).

 

[electrofelon]

..... a service rated gutter

I have never heard of such a thing.

 

[romex jockey]

I have never heard of such a thing.

perhaps 'gutter' is slang for wireway.

A service rated one is simply thicker steel

I use a lot of nema 3r serv rated wireways, makes it all neat

for more info, you'd have to download from hoffman
here's one>>

 

[MasterTheNEC]

That's just a wireway or junction box...nothing about that changes anything regarding the question and proper answer.

Paul W. Abernathy
Electrical Code Academy, Inc.
CMP #5 and #17

 

[romex jockey]

well you're free to question my install Paul, i'm far from infallable , in fact i already see a few no-no's (it's over a decade old)

I can tell you that, if i didn't bond the serv rated gutter, my ahj would not have passed it (it follows the HB pix)

Let me ask this, what in theory is the dif between an SSBJ and an MBJ , considering the predominant TN−C−S earthing system we have ?

Fwiw, what you see is a 3ph open delta w/high leg, pedestal is maybe 15' from serving poco pole

~RJ~