Equipment Grounding Conductor Size in SER Cable

Status
Not open for further replies.
E

Ethan1980

Member
Location
Salem, NJ
Occupation
Home Remodeling
This question came up when sizing wires for a single phase 100 amp sub panel. Why does the grounding conductor in SER cable seem to be quite a bit larger in size than is required minimum? Example, 1/1/1/3 SER. Going by table 250.122 the minimum size for 100 amp circuit is #6 AL so why does it come with #3? I'm wondering what I'm missing?
 
The only thing I can think of is that for a 3 phase service the bare conductor would be a neutral so they sized it for both situations.
 
mtnelect said:
I was referring to how the utilities have used the ground also as support for the drop.
Click to expand...
Yes but we are talking ser. It cannot be used as a drop to a building unless there is a guy wire to support the cable. Are you thinking quadraplex?
 
Dennis Alwon said:
Yes but we are talking ser. It cannot be used as a drop to a building unless there is a guy wire to support the cable. Are you thinking quadraplex?
Click to expand...
There is a theory that the ground wire should be insulated and not used as a support wire.
 
infinity said:
We think alike, that was my first thought but then the #1/0 minimum for parallels threw that out the window.
Click to expand...
Yeah sometimes I forget bout the 1/0 parallel min for a minute. I guess we could infer that of that was the reason, the EGC size would jump at 1/0 and beyond. There is also the "increased in size" provision which could happen for any size.
 
electrofelon said:
I like Dennis's three phase service idea. Don't think I have ever considered or seen SER used for a three phase service but nothing prohibiting it.
Click to expand...
That's absolutely the answer. It is after all "Service Entrance" cable, so I assume the standard sizes were originally chosen for applications where there is no EGC.

Cheers, Wayne
 
If the size of the bare ground the manufacturer uses in the SER is based on 3 phase with the bare being the neutral...how do they pick this #3 size? Other than the neutral cannot be smaller than the EGC and must be sized handle the unbalanced load, I don't see any requirements. It may not be always be appropriate to have #3 neutral with #1 conductors I would think. The GEC minimum for AL 1/0 or small is #6. I'm trying to understand pro/con running SER (1/1/1/3) or CU conductors in EMT. If I use CU, I can use #3 for hot legs, #8 Ground, #8 Neutral (if load is well balanced or #6 to be safer). Added benefit is harder to put a nail through EMT than SER. I am always more on cautious side but also don't want to be wasteful.
 
Ethan1980 said:
If the size of the bare ground the manufacturer uses in the SER is based on 3 phase with the bare being the neutral...how do they pick this #3 size? Other than the neutral cannot be smaller than the EGC and must be sized handle the unbalanced load, I don't see any requirements. It may not be always be appropriate to have #3 neutral with #1 conductors I would think. The GEC minimum for AL 1/0 or small is #6. I'm trying to understand pro/con running SER (1/1/1/3) or CU conductors in EMT. If I use CU, I can use #3 for hot legs, #8 Ground, #8 Neutral (if load is well balanced or #6 to be safer). Added benefit is harder to put a nail through EMT than SER. I am always more on cautious side but also don't want to be wasteful.
Click to expand...


This is true but in most cases the neutral can be sized smaller than the ungrounded conductors. If they cannot be then you will have to find another method. Here is southwire's chart for SER

1651707830610.png
 
wwhitney said:
That's absolutely the answer. It is after all "Service Entrance" cable, so I assume the standard sizes were originally chosen for applications where there is no EGC.

Cheers, Wayne
Click to expand...
Maybe. I don't know the history of SE cable. I've seen lots of old stuff in my career I don't think I've ever seen a three phase SER service.

Even for the parallel cables theory, the sizes seem hit or miss for when it works or not - in other words it doesn't work for all sizes even for just two parallel sets.
 
electrofelon said:
There is? 🤨
Click to expand...
The theory is called "Multigrounded Neutral". The utilities have combined the function of the neutral and the ground conductors into one conductor. This was the least costly solution to the problem with a voltage build up between the neutral and the ground conductor.
 
mtnelect said:
The theory is called "Multigrounded Neutral". The utilities have combined the function of the neutral and the ground conductors into one conductor. This was the least costly solution to the problem with a voltage build up between the neutral and the ground conductor.
Click to expand...
Ok yes I am very familiar with the MGN. Actually right now I am very much wishing the POCO had an MGN because I have a 2000' single phase primary run off a Delta system so I need 2 runs of 15kv CN instead of one, and at today's prices... 😤. But you still have me lost with these prior statements and what they have to do with an MGN or why it would matter if a "ground" is also a support....

mtnelect said:
I was referring to how the utilities have used the ground also as support for the drop.
Click to expand...
mtnelect said:
There is a theory that the ground wire should be insulated and not used as a support wire.
Click to expand...
 
Status
Not open for further replies.
Top