Can the neutral conductor be isolated on CPT

[Isaiah]

Does a CPT mounted within a combination starter 460-120VAC need to have the neutral
conductor grounded?


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[jim dungar]

You have a 2 wire CPT, technically it does not have a neutral.

Generally the NEC requires a system to be grounded when possible to keep the Line to Ground voltage <150V.

This will mean you will have a grounded conductor which needs to be white, so our industry slang is to call it a neutral.

 

[Jraef]

When I had a panel shop, I hired a wireman who had been in the Navy, he never grounded the CPT secondaries because he said they never did on ships. Drove me crazy because I couldn’t break him of that habit, so I had to make sure he didn’t leave it that way on every panel. I missed one once and it got out in the field that way. Kept getting trouble calls on it and people kept assuming it was grounded when troubleshooting. It was a mess until we figured that out.

 

[Isaiah]

You have a 2 wire CPT, technically it does not have a neutral.

Generally the NEC requires a system to be grounded when possible to keep the Line to Ground voltage
This will mean you will have a grounded conductor which needs to be white, so our industry slang is to call it a neutral.

So basically, would run the white wire to the neural bus within the starter and to the devices, such as HOA and Red “Run” Pilot LED on the control circuit.


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[don_resqcapt19]

250.21(A)(3) will permit the control power transformer to be an ungrounded system if you comply with all three requirements.
I prefer grounded control systems for the purposes of troubleshooting, and have only seen a couple of facilities where they used ungrounded control power transformers.

If you make it a grounded system, you apply Exception #3 to 250.30(A)(5) so you won't need a grounding electrode system and grounding electrode conductor.

 

[Isaiah]

250.21(A)(3) will permit the control power transformer to be an ungrounded system if you comply with all three requirements.
I prefer grounded control systems for the purposes of troubleshooting, and have only seen a couple of facilities where they used ungrounded control power transformers.

If you make it a grounded system, you apply Exception #3 to 250.30(A)(5) so you won't need a grounding electrode system and grounding electrode conductor.

Many thanks Don.


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