Splicing in junction boxes

Merry Christmas
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dlarkin

Member
Hi. In the spirit of full disclosure, I will say that I am not an electrical engineer or electrician. I am a civil engineer who does a fair amount of electrical design that is then checked by a third party EE.

That being said, I have had a disagreement recently with the EE and I wanted to see what people here might think.

The EE says that you cannot splice circuits in a junction box - the case in point being a branch circuit running from a breaker in a panel to a junction box and then spliced to conductors running to two separate loads (in this case lights on opposite sides of a room). My understanding was that as long as the JBox had adequate volume and is accessible that this would be ok, but he maintains that this is not allowed because one of the splices is a feeder which would require separate OCP.

He references 240.21 which states that "Conductors supplied under the provisions of 240.21(A) through (H) shall not supply another conductor except through an overcurrent protective device..." This certainly seems to support his case, but I can't see what would be the difference between this case and splicing two lights off of one lights wiring enclosure, as I think is often done in office overhead lighting.

Anyway, hopefully that's clear. I have searched and searched the code an other online resources, but I can't get this 100% clear in my head.

Thanks for any help!
 

iwire

Moderator
Staff member
Location
Massachusetts
As long as all the conductors are rated at least as high as the over current protection nothing in 240.21 applies.

The EE has to read the definition of tap conductors in 240.2
 
If all of the conductors being spliced in the junction box are of the same size (AWG) conductor, you are splicing. The EE seems to be thinking of splicing a smaller size conductor to the supply conductor which would be a larger size conductor. This may also be permitted, as long as all the conductors are protected by an overcurrent device as per 240.4/240.6.
 

dlarkin

Member
Thanks to you both. I think it will be impossible to convince him of this, but at least it makes me feel a bit less crazy!:)
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Tell him that this is a multi-wire branch circuit, that 240.21 does not apply, that none of the conductors are feeders, and that this is what junction boxes are for.

Added: Invite him to join this forum and pose his position here. We'll set him straight. ;)
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
The EE says that you cannot splice circuits in a junction box - the case in point being a branch circuit running from a breaker in a panel to a junction box and then spliced to conductors running to two separate loads (in this case lights on opposite sides of a room). My understanding was that as long as the JBox had adequate volume and is accessible that this would be ok, but he maintains that this is not allowed because one of the splices is a feeder which would require separate OCP.

This statement came from an Electrical Engineer?
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
And tell him, from me, speaking as an EE myself, that in a disagreement between an EE and a non-EE, on an electrical subject, there is no rule that says the EE will be right because he is an EE. That was one of my early lessons, in participating in this forum.

I agree with the other responders. The way I would put it is that 240.21 is about connecting smaller wires to larger wires, without putting an overcurrent device (i.e., to protect the smaller wire) at the point of connection. You are relying on an overcurrent device at the other end of the smaller wire to protect the smaller wire. It is a calculated risk, and you are required to reduce the risk by making the run short and by using conduit (or other means) to protect the smaller wire from physical damage.
 

Smart $

Esteemed Member
Location
Ohio
And tell him, from me, speaking as an EE myself, that in a disagreement between an EE and a non-EE, on an electrical subject, there is no rule that says the EE will be right because he is an EE. That was one of my early lessons, in participating in this forum.

I agree with the other responders. The way I would put it is that 240.21 is about connecting smaller wires to larger wires, without putting an overcurrent device (i.e., to protect the smaller wire) at the point of connection. You are relying on an overcurrent device at the other end of the smaller wire to protect the smaller wire. It is a calculated risk, and you are required to reduce the risk by making the run short and by using conduit (or other means) to protect the smaller wire from physical damage.
What I highlighted in red is typically true, but not absolutely...

240.21 is about splicing a conductor into a circuit (otherwise known as tapping) such that it has inadequate overcurrent protection at or ahead of its supply connection.

Typically a supplying larger conductor is an indicator the smaller tapping conductor is not adequately protected. Yet in cases where conductors are upsized to compensate for voltage drop, splicing a smaller conductor to a larger conductor may not be a tap.
 

dlarkin

Member
You guys are all awesome. Thanks for this. The person I am working with has a lot years in his field, so he is difficult to argue with. We have a policy at my company (Civil/Environmental firm) that an outside EE has to seal our electrical drawings, so occasionally I run into this kinds of disagreements with this person.

Anyway, your responses have been very instructive to me. Thanks!
 

dlarkin

Member
Oh, and to add my two cents on the "learned in school vs. not learned in school" discussion:

I would venture to say that 95% of engineers in any discipline are spending 95% of their work days doing things that they didn't learn in school, in some cases 100%. It is a curious thing about engineering school that you really don't learn very much useful stuff, although you do get a good background in theory and generally develop a pretty good work ethic and willingness to self-teach.

I just realized reading these comments that to some of you guys who maybe did trade schools or apprenticeships this probably doesn't make a whole lot of sense, since when you went to school or training you were most likely actually learning things that you could use once you completed your training.

It's one of the oddities of the engineer/tradeperson distinction that we currently have in these industries and is the reason that many engineers, especially new ones, don't know anything compared to a tradeperson in a given field. That's why forums like this are very helpful and provide some non-confrontational places for people like me to learn from people who actually make things work.

Anyway, thanks again!
 

mayanees

Senior Member
Location
Westminster, MD
Occupation
Electrical Engineer and Master Electrician
engineer bashing...

engineer bashing...

I have to chime in on the engineer bashing.. whcih I can do because I are one :)

I've seen a 30 year experienced EE, PE size a medium voltage motor feeder at the inrush current of the motor... or about 6 times the fla.
I've seen an experienced EE, don't know if he was a PE, but he worked for an engineering firm, size the motor feeder at the MCP amperage, or about 2.5 times the fla of the motor, as opposed to the correct ampacity of 125% with overload protection coming from the overloads.

Fortunately the tradesmen who install the design will typically call out the designer, thereby preventing the customer from spending unnecessary money from an inappropriate design.

But as is always pointed out in these discussions, a typical Electrical Engineering program does not include NEC. It's the responsibility of the engineer to learn it if he/she is practicing in that area.

And to the OP, I think it's time for your Civil-A/E firm to find another EE :)

John M
 
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