Help with Three Phase Panel Capacity

[michiganhotrod1]

Hello;
I need some help with capacity math on a three phase panel "upgrade".
I had a electric contractor replace the entire service drop and panel(s) on my garage building. It is three phase service, it was an old printing shop with separate 110V Direct Current in parts, and a 120/240 Volt A/C panel with fuses. I wanted to preserve the three phase capacity, upgrade, and get capacity for a few new 240 V circuts for a compressor, welder, etc.
The contractor replaced the 1940's stuff with a new drop, meter panel and a 200 Amp panel. However I lost every third panel slot to the "high leg", this was news to me. The original A/C fuse panel had circuits doubled up on one fuse, the contractor split each circuit to a separate 15A breaker, as he should have.
However the result is I have ONE single unused slot in the panel!
I am not talking to this contractor anymore.
I think I can use a circuit "chirper" to see if some of the old wiring is redundant or unused, and clean a few slots to run a 100A subpanel for my 240V needs.
Question: the three phase math hurts my head. I had some training in electrical installation but strictly residental stuff. How likely is it that I have overall capacity in the new panel to add the new load of a 100 AMP sub panel? I am not using any of the 480 service but I don't want to booby trap a future user. Is there any unique bonding requirement for the sub panel as a result of the three pase service?
Thanks for the help.
Mark

 

[Bert_]

Put all your 120v breakers in a 1 phase sub panel. Straight 240v 1 phase loads can use the high leg.

Installing a sub panel doesn't add any load.

 

[Norcal]

Put all your 120v breakers in a 1 phase sub panel. Straight 240v 1 phase loads can use the high leg.

Installing a sub panel doesn't add any load.

But the breaker must be rated for 240V, not 120/240V, if using the high leg, $$$.

 

[BillK]

What is hooked up to all of the breakers that do not have "labels" ??

Are you sure you have 480 ? Is there a transformer somewhere ?

 

[wyliesdiesels]

not enough to go on and your post is confusing to say the least

we need to know all loads you have and will have. and not just things like 240v compressor or 240v welder. that doesnt tell us what the HP rating on the motor is or what the input rating on the welder is

second off was the old service single phase 120/240v and you upgraded to 240Delta which means 120/208/240v? 208v being the hi-leg to neutral?

and you also have 480v 3Ø?

 

[Bert_]

But the breaker must be rated for 240V, not 120/240V, if using the high leg, $$$.

I've never had anyone push the issue.

Once a couple years ago I wired a commercial bin for an elevator. I met with the other electrician and he mentioned he had added a panel a few years before that should have some open spaces. I opened the cover and found a GE THQL panel fed with 480/277. His only comment was "the buss is the same". I kept all my stuff away from that panel !

 

[35Ford]

Why 240V Delta? Is that all that was available? Seems like an odd "upgrade"

 

[wyliesdiesels]

I've never had anyone push the issue.

Once a couple years ago I wired a commercial bin for an elevator. I met with the other electrician and he mentioned he had added a panel a few years before that should have some open spaces. I opened the cover and found a GE THQL panel fed with 480/277. His only comment was "the buss is the same". I kept all my stuff away from that panel !

you do realize slash rated breakers are not rated for the fault current above 120v?

 

[Bert_]

you do realize slash rated breakers are not rated for the fault current above 120v?

Yes. But it's been done thousands of times and nobody makes an issue of it.

Kind of like 10hp motors on 10-50 plugs.

 

[Bert_]

Why 240V Delta? Is that all that was available? Seems like an odd "upgrade"

240 delta is great if you are mostly motor load.

 

[michiganhotrod1]

What is hooked up to all of the breakers that do not have "labels" ??

Are you sure you have 480 ? Is there a transformer somewhere ?

The unlabeled circuits are the old unlabeled fuse panel circuits. I need to sort out the loads but typically they are either lighting circuts or power to three or four 120V outlets each circuit. I screwed up on the three phase, it is a 120/208/240 four wire service. It had a rectifier feeding a 120V DC series of circuits to power printing presses.

 

[Norcal]

The unlabeled circuits are the old unlabeled fuse panel circuits. I need to sort out the loads but typically they are either lighting circuts or power to three or four 120V outlets each circuit. I screwed up on the three phase, it is a 120/208/240 four wire service. It had a rectifier feeding a 120V DC series of circuits to power printing presses.

It is either 240/120V, or 208/120V, it is not both and by the layout it is 240/120V 3Ø panel.

 

[wyliesdiesels]

The unlabeled circuits are the old unlabeled fuse panel circuits. I need to sort out the loads but typically they are either lighting circuts or power to three or four 120V outlets each circuit. I screwed up on the three phase, it is a 120/208/240 four wire service. It had a rectifier feeding a 120V DC series of circuits to power printing presses.

what do you mean you screwed up on the 3Ø? what you have is 240/120 Delta. The 208v is the hi-leg voltage to neutral which is not useable and the reason why your panel has no single pole breakers in the B phase

 

[michiganhotrod1]

Thanks for the input so far, as mentioned former DC hi-leg/ Delta stuff confuses me and was a surprise when the panel was installed.
I want to run the following 240V items, a 15Amp IR compressor, a Miller Map gas welder needing a 50Amp breaker, and a future 20Amp lift. So a 100 Amp 240 volt sub panel should fit my needs, right?
The original 1940's A/C fuse panel was only 120 Amp, 120 volt only, and except for one added outlet it is the entire load currently on the new 200 Amp panel. The electricians left the old panel in place and used it as a big connector box. As mentioned some of the old circuits were fused for convenience I think since they only have 3 or 4 outlets connected since the outlet wiring is run in conduit underneath the concrete floor.
So if I get enough "stuff" off the new panel to fit a 100 Amp breaker for the sub panel I should be OK, right?
Is there any unique bonding requirement needed due to the Delta?
Am I missing anything?
It is hard to get soemone else to do another electricians work and I have done regular sub panels in the past, garages, etc.
Thanks.
Mark

 

[wyliesdiesels]

you dont need to put all your 240v equipment on a separate panel. there is no risk of smoking it by connecting it to the hi-leg. the separate subpanel would be for 120v loads.