What would you do with this mess? (Pictures)

Status
Not open for further replies.
D

donw

Senior Member
Location
Arizona
I am doing the engineering for a tenant improvement of a church hall built in the 60s. The service to the building is a feeder from a 1600A 120/240V 3-ph high-leg SES in another building. The disconnect in the SES is 600A with 400A fuses. 2 of the legs are 2 sets of 400MCM Al, and the 3rd is 2 sets of 1/0 Al (yep, the present 400A fuse doesn't protect this leg). The Neutral is 2 sets of 1/0 Al, and there are no equipment ground conductors. The conduit going into the ground is metallic, but I bet it turns to PVC. I was told that at one time the service was directly from a utility transformer instead of fed from the other building. I am estimating that the additional kitchen equipment and A/Cs will push the load on the main legs over 400A, and the third phase to around 200A. I am considering increasing the main two fuses to 500A and lowering the third to 250A, and requiring a #2CU equipment ground to be pulled in each conduit. The pull section and landing lugs should be replaced with a 600A, and the conductors in the gutter upgraded to 2 sets of 350MCM CU for each phase and a single 350MCM CU for the high leg. I don't see a good connection to the building grounding electrode, so I will require connection to piping and a ground rod. Am I missing anything?
CIMG6253small.JPG


CIMG6244small.JPG
 
I get the feeling the equipment is older than that wall its on? Other than that, I'm not quite sure I can find anything wrong with it - other than it's inherent lack of beauty, and not being sufficient for the load you intent to add. Can't tell about the grounding, but if it were once a main one would assume it had one at some point, and may not have been required when the change was made to the install. In the picture there are some bonding bushing and a bare split-bolt to something, where does it go? They say the conduit is RMC - it should be easy to check by running a jumper to the outher side and checking continuity.
 
e57, thanks for the reply. That's a good idea for checking the continuity. Wouldn't you say that the "high leg" conductor is under sized for its fuse? And I think the conductors in the gutter are undersized to be protected by the fuzes - 2 sets of 1/0 Al per phase.
 
what size pipes are these

what size pipes are these

Looks like 3" from NY.

I would not rely on a continuity tester to ring to verify the pipe is rmc all the way. If it were to change over to pvc it would probably happen within 10 feet give or take a manufactured elbow.


You could also go to compact conductors to maximize ampacity for the pipe size and do the right thing for the big guy.
 
quogue, I would at least have the aluminum replaced with same size copper - that would give them 600A. But they are extremely cost sensitive.
 
donw said:
e57, thanks for the reply. That's a good idea for checking the continuity. Wouldn't you say that the "high leg" conductor is under sized for its fuse? And I think the conductors in the gutter are undersized to be protected by the fuzes - 2 sets of 1/0 Al per phase.
Click to expand...
Thought you said the high-leg didn't have a fuse? Then, wouldn't be able to tell without knowing whats on it... That said the neutrals could be undersized as well, as both are reduced. As for the lack of EGC's - conduit is acceptable for that purpose, although many would debate that seeing the state of the equipment. And there just may be a rod or ufer that you have not found yet. But after your calc', you sound capable enough to know whether it should stay or go, but I think many would opt fo go, and start fresh just to eliminate the unknowns.
 
High leg does have a 400A fuse - for 2 1/0 Al! I want to replace that with a 250A fuse. Good point about the neutral. I'm not really sure how to estimate the imbalance, except for the new circuits I'm adding.
 
Ah... So you are looking for more info on the load calc'... First I would suggest you look into the examples in Annex D (Say D3...) which will always point you into Art. 220, neutrals are 220.22, the high leg will be calc'ed at 240 for the connected load, as it is only to be used as one half or third of such circuits.

But if this is a liability issue - you may want to pass on this calc to an Electrical Engineer if you are not completely comfortable with the task... JMO... As you are dealing with a complicated and sizable feeder/load, demand factors, reduced conductors, parallel runs, and existing questionable equipment. A lot of variables. Missing an element of this could cost you more than his fees....

And yes, the fuse for the high-leg is too big for the reduced size conductors. (not knowing the insulation or termination rating can't say what it should be) Look into 310.4, 310.15 and table 310.16.
 
Last edited:
e57, as I said in the first post, I am the engineer. I'm just not sure how to estimate the imbalance of existing loads. When I design from scratch, I always use "full sized" neutral conductors, but this one is existing.
 
220.22..... Wait - HMMMM.... are you an Engineer that doesn't have a code book? :rolleyes: The first sentance (and rest) of that code is really clear.

Not to be meant as a personal attack, but this is really easy. If you can quote me that first sentance to make me feel better.
 
Sorry 'bout the number change.... (I don't have to get a new code book for 6 more months) The wording is nearly the same... But sounds like you found it.
The maximum unbalanced load shall be the maximum net computed load between the neutral and any one ungrounded conductor,
Click to expand...

Add up all the single phase loads for each phase, the highest phase wins... :wink: Next size up, although better judgement would say go bigger... And the rest of that code tells you what systems you should add a factor to, or what systems you can not reduce. In your case, look at 220.61B2 as it sounds as if you have possiblity a portion over 200a to apply a 70% demand factor to.

Easy huh?
 
Correct me if I am wrong, but a couple of items.
The supply is 2 conductors to the old CT can, with one set installed into the trough?

The lugs for this installation are definitely not properly installed, and with the addditional load you have mentioned, this may become an issue. I would consider changing the termination to a new detail or polaris type terminations.


And the new installation should include identification of the different disconnects.
 
Last edited:
Pierre, there are 2 sets of 400MCM AL to the pull section and then 2 sets of 1/0 AL to in the gutter (for the main two phases.) The high leg has 2 sets of 1/0 AL and 1 1/0 CU in the gutter. What are "detail" or "polaris" terminations?
 
What would i do with this mess?If i had to put a stamp on this i would certainly consider replacing the whole mess with a new 600 amp main breaker w/p panel,upgrade all three phases with 350 cu and replace the fuses with 600's.This would eliminate all the splicing, and provide future load capability, and neating(is that a word) up all the pipe work.It looks as if three of the existing disconnects need to be replaced anyway.(they appear to be nema 1).
Rick
 
Status
Not open for further replies.
Top