Grounding/Bonding Single Phase 2W Transformer

Status
Not open for further replies.
B

bozosboss

Member
A small single phase, 480V-120V, 2W secondary, dry type transformer is fed from a CB in a 480V MCC lineup in an industrial plant. The transformer, in turn, feeds a CB panel with main. Isn't it proper to bond the neutral to ground at the transformer only,and have the neutral bar in the CB panel isolated from the panel? The CB panel ECG would then be the RMC that is connected between the transformer case and CB panel.
Is such a dry type transformer in an industrial plant treated as a "separately derived system" per the NEC Art. 100 of such a system?
 
Re: Grounding/Bonding Single Phase 2W Transformer

It is an SDS and the bonding and grounding electrode conductor connection can be made either at the transformer or the first OCPD, but not both.Don
 
Re: Grounding/Bonding Single Phase 2W Transformer

Don, thanks for the reply. I have found that in this particular facility it has been common practice to bond the neutral and ground at the transformer and also at the panelboard. No seperate EGC is routed from the transformer to the panel but they are connected via RMC. In the panel the neutral is then bonded to the panel frame.
 
Re: Grounding/Bonding Single Phase 2W Transformer

As don_resqcapt19 says, it sounds like a SDS to me.

But, the way it is worded, I might question some of this common practice at the facility you speak of.
 
Re: Grounding/Bonding Single Phase 2W Transformer

I don't believe this changes anything, but to describe the system a little better - primary feed is via 13.8kV to individual substations where it is stepped down to 480V, 3ph., Delta/Wye, with high resistance grounding. Metal enclosed switchgear is typically used with d/o type power circuit breakers to feed multiple indoor motor control centers (MCC).
The MCC buckets are combination starters for motor loads and MCCB's for feeders to various loads such as the single phase transformer and panelboard.
The feeder from the MCC to the transformer is typically routed in RMC and may or maynot have a seperate EGC (sometimes the RMC only is used for the EGC).
At the small (typically 15kVA or less) dry type transformer secondary the neutral ( for say a 1 ph., 2W system) is bonded to ground and I have found, that where the transformer feeds a breaker panel, the neutral is also bonded to the enclosure. I questioned this and was told it is "common practice" in this plant.
 
Status
Not open for further replies.
Top