480V delta source for 480V wye system? 1

[robbm]

We have a system that is designed for a 480V wye system, and the customer came back stating that their power source has 1 leg grounded (ie delta). Not having dealt with this in awhile, do I just need to make sure any 3phase devices are rated for running off 480V delta?

Regarding the devices on the system - there's a pump, 3phase electric heater, and a 480-120 transformer on the system:

The pump is running off a soft start (AB SMC-3) that is stated in the manual as having an "inside delta connection" so I think I'm good sticking with that as-is - there's just a dipswitch and separate wiring instructions it seems (assuming we're using a delta-connected motor).

The heater is controlled by a SSR and its documentation mentions hooking up to delta loads, so that should be fine too.

For the transformer, as long as I 480V between the legs going to the transformer primary terminals, i should be fine, right?

I'm told the end user is looking into a 480V-D to 480V-Y transformer, to eliminate any need for us to change anything, but want to know ramifications in case they don't go that route. Thanks in advance.

 

[cranky108]

For a 480 system, all wiring devices should be rated for 600V, at least in the US. If you have surge devices that would be a concern.
Can you lift the neutral without a problem to other devices or customers?

What devices do yo have connected phase to ground? Maybe a meter, so you would want something like a 2.5 element meter.

 

[jraef]

Delta SOURCE and delta LOADS are not the same thing. There are several issues with regard to having a delta SOURCE. All circuit breakers must be rated as "straight 480V" (to use the common vernacular), that's as opposed to being "slash rated" as in 480/277V. Most small inexpensive circuit protective devices are going to be slash rated for 480/277V, because the potential asymmetrical fault energy in the circuit is lower, so the device can be made cheaper. This doesn't apply to fuses, but it may apply to some fuse HOLDERS as well. It has to do with the "withstand" rating; basically the physical strength of the plastic parts.

Many power electronic devices also cannot be safely connected to 480V delta SUPPLY systems, because their internal components are selected based on a maximum voltage potential to ground of 277V. The A-B SMC-3 is fortunately not of that ilk, they CAN be used on delta supplies. But again, you must look carefully at the breaker feeding it (if any).

Without knowing what the SS controller is for the heaters, it's impossible to advise you. The delta-wye transformer option is the "safe bet" if you are worried. It's done all the time because most VFDs cannot handle being connected to delta supplies (without consequences). So you will easily find those transformers by looking for what are called "drive isolation transformers"; delta input, wye output, 1:1 ratio.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[waross]

I would be taking a close look at the SSR and heater connections.
I see a lot of 480/277 Volt heat tracing in the field. The SSRs are good only for 277 Volts.
I see a few 600/347 Volt SSRs but often a plant with 600 Volt supply will have dedicated 600/480 Volt transformers or 4160/480 Volt transformers to feed the heat tracing. (600 Volts is standard in Canada rather than 480 Volts).
I realize that there is a whole world of SSR heating applications outside of my experience, but based on what I see in the field I would be taking a close look at the SSR ratings and connections.


Bill
--------------------
"Why not the best?"
Jimmy Carter