Commercial 3Phase Service

I’ve done several commercail walk through inspections, mostly store front operations with typical services and situations.
Today I ran into a 3-Phase electrical service drop for a small auto-body repair operation. Panel and all outlets looked fine, just wondering if anyone had any tips on viewing this type of service and identifying voltage and amp capacities.
Appreciate any feed back.
Thanks Jack

Hi Jack,

I do mostly commercial work and see many 3 phase panels, I normally have an industrial electrician evaluate these systems especially if there is equipment running on all 3 phases such as elevators, compressors, lift or production equipment.

Its fair to say that few inspectors are knowledgable enough for 3 phase (particularly grounding and bonding of equipment) and very few residential electricians are familiar with commercial wiring. It is a good example when to use sub contractors on commercial inspections.



The difference between commercial and residential has more to do with the wiring methods employed than the number of phases.
You are also a lot more likely to be dealing with classified areas, egress lighting and separate motor starters.

There are quite a few differences, depending on the size and application of the commercial or industrial load involved, but the same principles apply - wire size, panel nameplate rating, etc. However, as the size goes up, fewer HIs will likely have the ability to properly evaluate the service. In adiditon, once beyond the service entrance, there can be many things that you will never see in a home setting. If evaluation of such a facility is needed, the electical system is often a significant study alll by itself.

i will echo both guys’s comment with commercal 3 Ø system there is alot more to dealt with this than the resdentail system is and the voltage system is far more wide varies and some case some building will have more than two voltage system in there that can compound it if you dont catch it fast

typically like this 480Y/277 volts and 208Y/120 this is the most common voltage you will intercounted but there is other voltage i will list it in a sec

the other one is what we called delta system this can get tricky depending if it have 3 or 4 wire system

3Ø3w typically either 240 or 480 volts

4W typically have 120/240 volt but one phase to netual will have wildleg you can call other words if you want to ] that will be 190-208 volts depending on type of transformer set up

that type of connection you need a extra attetion with this sytem therefore they will mark this conductor in ORANGE and marked very well with it

but i will give you a head up in old delta system there are some area they will marked in RED that was used in before 70’s era i think if i recall it right

i hope i did expain this pretty clear on this

Merci , Marc

I avoid switching equipment like the plague. I’ve got a great commerical electrical contractor who handles the larger stuff for me…

Here’s todays equipment room:

I won’t try to go into it here for reasons mentioend above, but 3 phase 4 wire circuits as used in industry today very seldom have an ‘open delta’ or ‘red leg delta’ as mentioned. Some utilities furnish service that way, however, for loads that have only a few 3 phase applications

Looks like a Ryco metering switchboard. :smiley: Beats a gutter and hanging a bunch of metercans

I still see “red leg” delta here in Florida. If you ever get to Key West go to the Hogs Breath Salloon and look at the pole serving them and about 5 other places (behind the stage in the parking lot). That is a 3 phase red leg using 3 transformers, pretty rare. Usually it is “open vee” using 2.