Changing Wire Size in the Middle of a Circuit

[DM2-Inc]

We had a helper installing some wire for a fire alarm system. Apparently he was new enough that he couldn't recognize the difference between 16 AWG and 18 AWG (it could have been 14 and 16...I'm getting mixed information from the field). As a result, one circuit has one leg at the larger AWG and the other leg at the smaller AWG. There is a fair amount of work in involved in correcting the mistake and I'm struggling with replacing the wiring or leaving it alone, considering the cost in labor, not to mention the lack of professionalism.

I believe there is a section of the NEC which prohibits stepping down a circuit more than 1 wire size, but can't remember where I found this. I have found nothing that specifically states that you can't have have on leg of the circuit installed with a larger wire than the other leg.

 

[don_resqcapt19]

There is no such "step down" rule in the NEC. As long as the conductor is large enough for the load and is protected at or below its ampacity, there is no code issue. If this conductor is part of an horn or strobe circuit, there may be voltage drop issues that you will have to check for. Too small of a conductor could drop the voltage below the minimum permitted voltage for the horn or strobe.

 

[Ragin Cajun]

How much work to redo vs the time to analyze, verify, explain to AHJ, engineer, owner, fire marshal, etc.??

I feel your pain, a mess either way!

RC

 

[DM2-Inc]

Don,
Thanks for your reply...and I'm guessing you are unaware of any requirement about using 2 different wire sizes for a circuit as well?

Ragin,
If the measure of the performance of the field helper, and his supervisory, is any indication of the hours (not cost as I've got to believe we can't, or actually shouldn't, be paying that much)...you're right...I keep dishing this off to the project manage and he keeps coming back to me with the same question...as some point in time, without doing a time & motion study, it's going to be cheaper to replace it. On the other hand this is a prefabricated building, going out of the country so I don't have anyone breathing down my neck, and likely won't have...It's just embarrassing. To me it's more a question of what one's dignity and reputation are worth...If I can keep my name out it...well...you get the point...

 

[charlie b]

I infer that this wire is for the alarm signals. Is that right? If so, I don't see a problem with having two different wire sizes, so long as the smaller wire is big enough (i.e., the voltage drop issue mentioned earlier).

This would be a slightly more interesting situation, if we were talking about the branch circuit that powers the alarm panel. I know you wouldn't be dealing with 14s, 16, and 18s in that situation, but let's play with the notion for a moment. Suppose you had a 30 amp, 240 volt, single phase circuit served by a two pole breaker. Suppose you used a #10 for one of the ungrounded conductors and a #8 for the other. How would 250.122(B) come into play?

{NOTE: If this side issue starts much of a discussion, I will move it to a thread of its own.}

 

[JDBrown]

I infer that this wire is for the alarm signals. Is that right? If so, I don't see a problem with having two different wire sizes, so long as the smaller wire is big enough (i.e., the voltage drop issue mentioned earlier).

This would be a slightly more interesting situation, if we were talking about the branch circuit that powers the alarm panel. I know you wouldn't be dealing with 14s, 16, and 18s in that situation, but let's play with the notion for a moment. Suppose you had a 30 amp, 240 volt, single phase circuit served by a two pole breaker. Suppose you used a #10 for one of the ungrounded conductors and a #8 for the other. How would 250.122(B) come into play?

{NOTE: If this side issue starts much of a discussion, I will move it to a thread of its own.}

That's a fun one, Charlie! Which section takes precedence: 250.122(A), which says "... in no case shall they [EGCs] be required to be larger than the circuit conductors ..." or 250.122(B), which requires the EGC to be increased in size proportionally to the ungrounded conductors?

Personally, I would say both requirements would be satisfied if your #10 leg has a #10 EGC and your #8 leg has a #8 EGC. But I can see how someone else might take a different view.

To the OP: I agree with what has already been said. If the smaller gauge wire is acceptable (ampacity and voltage drop) then there's not going to be a Code issue with leaving it as is. Whether or not you want to change it as a matter of personal pride in your work is a personal decision.

 

[DM2-Inc]

Thanks for the input everyone..

Fortunately the wire is for an initiating device circuit and the wire lengths are extremely short...just a lot of devices. As a standard, we use 14 AWG on all notification appliance circuits. Most of the systems we provide are in small buildings with no more than 5 notification appliances and 300 feet of wire.

Of course there have been those cases were a designer failed to do a voltage drop calc with 20 notification appliances and most of the strobes set at 75cd or better...

I think we'll...
1. Leave the wire alone...
2. beat the helper severally about the head and shoulders...
3. educate both the helper and his senior installer on wire sizes...

I'm sure we can do more in terms of training and educations. It's unfortunate that most lessons seem to sink in better as the result of a mistake...In the words of the comedian; Dennis Miller, "...that's just my opinion...I could be wrong..."

 

[charlie b]

That's a fun one, Charlie! Which section takes precedence: 250.122(A), which says "... in no case shall they [EGCs] be required to be larger than the circuit conductors ..." or 250.122(B), which requires the EGC to be increased in size proportionally to the ungrounded conductors?

Personally, I would say both requirements would be satisfied if your #10 leg has a #10 EGC and your #8 leg has a #8 EGC. But I can see how someone else might take a different view.

But I was speaking of a single circuit, so there would only be one EGC. Perhaps we would need to upsize it to #9? :lol:

 

[iwire]

Perhaps we would need to upsize it to #9? :lol:

I will need to ask my supply house for some 9 AWG green.

 

[JDBrown]

But I was speaking of a single circuit, so there would only be one EGC. Perhaps we would need to upsize it to #9? :lol:

:slaphead: I must be having an off day today; for some strange reason I was thinking of a series loop, rather than a regular 2-wire circuit in conduit. Not sure where that came from, as I haven't dealt with anything like that since college.

I return to my initial reaction of this being a fun conundrum.

And I don't think a #9 would cut it -- that would violate BOTH rules, instead of just one or the other.

 

[jcassity]

im sure this is solved by now,,
i cant see how it is costly to
-disconnect each end of the suspect conductor
-secure any splices that may have occured with tape
-tape your new pull to the suspect run of wire
-use the suspect wire to pull in your new run
-connect each end

-for life / safety circuits, i mandate home runs to each end, its just the right thing to do