Step up transformer install question

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bzzzbzzz

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electrician
Hi all. I'm working on a job installing a 30kVA 240-480 volt three phase transformer for a clients machine that doesn't need a neutral. The primary is 240 volt three phase witha high leg. I'm wondering if I need to ground the H0 connection on the 480 volt secondary. Right now I have 477/480/470 volts phase to phase but some weird voltages to ground. I have an equipment ground coming in with the primary, an equipment ground on the secondary, and a grounding electric conductor to cold water copper, all terminated on a terminal bar. Thanks in advance for your help.
 
A lot of equipment does not like ungrounded systems and I see no harm in your bonding HO and there are positive reasons to do so..
You do need to review the grounding electrode requirements for a SDS, 250.30.
 
bzzzbzzz said:
Hi all. I'm working on a job installing a 30kVA 240-480 volt three phase transformer for a clients machine that doesn't need a neutral. The primary is 240 volt three phase witha high leg. I'm wondering if I need to ground the H0 connection on the 480 volt secondary. Right now I have 477/480/470 volts phase to phase but some weird voltages to ground. I have an equipment ground coming in with the primary, an equipment ground on the secondary, and a grounding electric conductor to cold water copper, all terminated on a terminal bar. Thanks in advance for your help.
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Always ground the secondary whenever you can. It establishes a firm voltage to ground, which among other benefits makes it easier for troubleshooting (as you have experienced).
 
so it's a delta/wye 240/480? you need to ground the HO neutral of the secondary as you would a service. Separately derived system. Bond to nearest steel also or... .
 
If the machine would happen to have any VFD's they might not like it if you don't have a solid ground on the secondary neutral.

Bonding the secondary neutral will make it have a pretty consistent ~277 volts to ground.
 
kwired said:
I'd guess not, especially if he has 240 primary volts.
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I'd guess most likely not, Either way it should be grounded just like most SDS. But it's a good vid and it addresses characteristics of a WYE and how the voltages become unstable. I use the vid to explain to younger guys who want to learn. The guy does a good job of explaining it
 
Is the secondary Wye connected?
If so you are required to have a SBJ to ground
Sorry I answered and didn’t post. I had a 480V motor controller, the control power secondary was not grounded. It was very difficult to TS the control wiring as there was no ground reference
 
electrofelon said:
Only thing I am not clear on is what happens if you make the evens the secondary wye point instead of the odds?
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Nothing electrically, except the bushing of the terminal you want to use as the neutral won't line up with the terminal on the can.
 
Now that I think about it, if I remember correctly, they use the left and center bushings in wye systems here, so they do use what would be the even numbers as the wye neutral. It'll work either way.
 
LarryFine said:
Nothing electrically, except the bushing of the terminal you want to use as the neutral won't line up with the terminal on the can.
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Right, I dont see what it would do electrically, and I didnt follow his brief reasoning for making it the way he did. I dont follow your statement either. Are you saying you just want the primary and secondary neutrals to be in line with each other?
 
No, I am saying that each can has a grounding terminal below the center secondary bushing.

That bushing is used as the neutral, regardless of whether the left or right bushing is the line.

As long as all three units are wired the same way, it doesn't really matter which way it's done.
 
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