Electrical service clarification

Try measuring.

You’re right Bob. A meter would have resolved this. If you will indulge me, I will continue to try to exhaust what information was visually ascertainable. Which in my estimation I have reached that point, but I am not an electrician.

“Normally” A-C single phase with a neutral from a 4-wire delta will give you 120/240 volts. In this case you would use A-B because C is the high leg.

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We would be able to identify the connection if we had a clear picture of the transformer connections. The picture Brian posted is not from a good angle and it is not clear enough for me to be able to trace the conductors.

Brian didn’t mention what the facility’s primary use is. The building’s use weighs heavily into electrical design considerations. The electrical system is most likely 3θ/4w 208/120Y. It could be a Delta connection, but that would be unusual for most commercial buildings.

Commercial buildings that are mainly offices and retail are not as likely to use a Delta configuration as one where there is a lot of machinery and heavy equipment.

It was mentioned somewhere in this discussion about not being a Delta connection because of the lack of a high-leg. Most Delta connections do not have a high-leg. Delta transformers can have a center tap, a corner ground, or none. Only center-tapped Deltas have a high-leg. They are relatively rare.

Delta connections are also more prevalent on primary connections than on secondaries. Delta primaries with Wye secondaries are more popular than Delta/Delta.

Also, this particular installation is a set of pole mounted transformers and a service mast. That makes it all the more less likely to be a center-tapped Delta.

Of course, anything is possible and we simply don’t have enough information to say conclusively. The main area that we need to see is the transformer connections. If it is a center-tapped Delta, the high-leg will be identified in the panel, so an interior view of the panel would tell us that.

3θ/4w 208/120Y is the most common configuration because of its versatility and relatively low cost. Based on the information provided, I’d put my money on it being 3θ/4w 208/120Y. I’m basing my guess on what is most common. If we can get a good picture of the transformer connections, we will know.


Unfortunately, that’s all I have on the transformer. Lesson learned.

The purpose of the building is an auto body repair shop. The three phase is specifically for the paint booth. Owner stated the utility provider had to modify electrical service to accommodate the three phase system. Which the owner had to pay for.

Thanks for the feedback!


I found another photo. It may be too pixelated to be of help.

Green arrows are pointing to the subject property service conductors.

An volt analyser.

A simple voltmeter wouldn’t tell you the voltage?

It looks like a 4-wire drop and 3 single phase transformers most likely wired 4-wire Delta.

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Thank you :+1:

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Brian, I can’t see the conductors clearly enough to know what the connection is. I grabbed a few images from the internet and added annotation to them so you can see the differences among common connections: Delta, Center-tapped Delta, and Wye (with and without a neutral).

Notice that the Wye connections all have one side of each transformer connected together. It can be either the right or left side. That’s the easiest and quickest way to identify a Wye hook-up. There will also be two conductors coming from one of the transformers. The second conductor is the grounded (neutral) conductor. It can come off any of the three transformers. It doesn’t matter which one.

With a Delta connection, the secondary coils are connected in series with a tap off each corner, so there is one conductor that jumps from the first transformer to the third transformer. A Corner-grounded Delta will have a second conductor connected to one of the three phase taps. I do not have an image of a Corner-grounded Delta.

A Center-tapped Delta will use the center bushing of one of the three transformers for the neutral (it doesn’t matter which transformer). I couldn’t find an image online of a Center-tapped connection, so I drew a red line to show where it would go on one of the diagrams.

In a body shop, small, machine shop, light manufacturing, etc, they could go any way they want with their transformer connections. Sometimes, a Delta service will be installed and supplemented with one or more transformers to serve the facility’s less common loads. For example, a manufacturing plant may buy electricity in bulk and redistribute it internally using substations and small distribution networks on separate transformers. A machine shop might have a Delta service, but may install one or more small transformers to handle lighting circuits, convenience outlets, small appliance circuits and so on.

The decision on which way to go is usually based more on money than engineering considerations. Small shops, restaurants, and small retail stores usually pay full retail for electricity. They tend to have rather basic electrical systems. Based on your photos, I’m sure that that is the case with this customer. Regardless of whether the service is Delta or Wye, it is a simple matter to provide any needed voltage or configuration by adding a few small dry type transformers where needed.

The possibilities are endless. Most small consumers of electricity rely on their electrical contractor to give them guidance and make recommendations. That’s probably OK for very small consumers of electricity, but larger consumers should hire a consultant who is familiar with the local utility tariffs and who can make specific recommendations.

In my experience, most small non-residential customers pay too much for electricity. They often are not aware of the many options available to them. In general, the higher the Voltage, the lower the cost of electricity. Also, most small to medium sized businesses rarely pay close attention to Power Factor. Residential consumers are not charged for poor (lagging) PF, but commercial customers can incur some big penalties for a low PF. There’s usually no credit for a leading (>1) PF though.

That’s probably more than you want to know. I mentioned all those things though because small businesses tend to make costly mistakes when it comes to electricity and electrical systems.


Not at all! I’m looking forward to digging in and digesting all of it.

Thanks for taking the time to present this “class” on electrical service!


George Wells, “You’re The Best!”

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