Is an EGC needed for surge suppressor (strip type) operation

[art]

I have a 120 V output from the secondary of a transformer. I plan to connect to a receptacle to plug the strip into. I know a short circuit or overload will open the fuse on the primary. Will grounding one end of the secondary clear a ground fault? Can that connection to the ground bus also act as the neutral for the receptacle?

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[paulengr]

Not enough information to say if it will trip a fuse especially on the primary side. In fact usually trying to get primary protection to double as secondary is nothing but trouble.

Two scenarios on the transformer. If it is a separately derived system you ground the neutral to an effective grounding system and the connection is the system binding jumper. Or you connect a secondary leg (assuming this is single phase) to the bonding on the primary side effectively extending the existing grounding to the new voltage. Floating (no neutral) systems are illegal by NEC at 120 V, and strongly discouraged by HSB and FM (major business loss insurance carriers) to put it mildly.

 

[art]

Thanks for the prompt response.

So, I connect one side of the secondary to the ground bar. Then, run from there (a neutral?) as the return from the receptacle. Then, connect the EGC to the ground in the receptacle.

I'll add a fuse to the ungrounded leg of the secondary

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[paulengr]

Thanks for the prompt response.

So, I connect one side of the secondary to the ground bar. Then, run from there (a neutral?) as the return from the receptacle. Then, connect the EGC to the ground in the receptacle.

I'll add a fuse to the ungrounded leg of the secondary

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You are mixing some things here.

This would be a separately derived system and needs its own ground rod(s). Tie into existing ground only to meet common service requirements. The key word here is separate. Treat it like the primary side is a “utility”. As such you fuse or breaker both poles on the secondary. There are engineering arguments about common ground grids but NEC stresses separate ones. One of the issues is you are creating another path to ground through the new transformer rather than back through the system bonding jumper which can only exist in one place at 120 V. Another is since they are not isolated surges on the higher voltage side affect the lower voltage side. I’m guessing though you are going from say 480 or 240 to 130, not say 4169 to 120. The easy (and cheap) way to do this is an auto transformer where by nature your neutrals are automatically “jumpered” since it is the sane terminal.

Jumper from the primary side neutral to the secondary neutral. Keep grounds separate, IF you have access to a neutral. Otherwise see above. This just makes it an extension of the higher voltage system. Think of how an AC “wall wart” works...the load is just a load even though it’s behind a transformer. And we carry the bonding through as a continuous isolated system.

 

[art]

You are mixing some things here.

This would be a separately derived system and needs its own ground rod(s). Tie into existing ground only to meet common service requirements. The key word here is separate. Treat it like the primary side is a “utility”. As such you fuse or breaker both poles on the secondary. There are engineering arguments about common ground grids but NEC stresses separate ones. One of the issues is you are creating another path to ground through the new transformer rather than back through the system bonding jumper which can only exist in one place at 120 V. Another is since they are not isolated surges on the higher voltage side affect the lower voltage side. I’m guessing though you are going from say 480 or 240 to 130, not say 4169 to 120. The easy (and cheap) way to do this is an auto transformer where by nature your neutrals are automatically “jumpered” since it is the sane terminal.

Jumper from the primary side neutral to the secondary neutral. Keep grounds separate, IF you have access to a neutral. Otherwise see above. This just makes it an extension of the higher voltage system. Think of how an AC “wall wart” works...the load is just a load even though it’s behind a transformer. And we carry the bonding through as a continuous isolated system.

I'm bringing in 240 into a subpanel so I don't have a primary neutral. Also have the EGC to the ground rod. Is the case bonded there?

The secondary is 120 (no center-tap, so no neutral either)

Earlier, I understood I could not have the 120 floating and had to ground (bond?) one end of the secondary.

That's where I'm at. Your help is very much appreciated.

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[paulengr]

I'm bringing in 240 into a subpanel so I don't have a primary neutral. Also have the EGC to the ground rod. Is the case bonded there?

The secondary is 120 (no center-tap, so no neutral either)

Earlier, I understood I could not have the 120 floating and had to ground (bond?) one end of the secondary.

That's where I'm at. Your help is very much appreciated.

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With no neutral you make it a separately derived system.

You establish a neutral by grounding a phase conductor in a separately derived system. It does not have to be a center tapped transformer. In fact some 480 systems are corner grounded although quite often this is a retrofit.

The case can be bonded either way and there are times when you want “station” (primary) grounding but typically it is grounded to the secondary side bonding, Read NEC rules carefully but again you must provide a system bonding jumper to your neutral and you must ground the ground bus/bonding but there are two choices. You can do it at the transformer or at the new “main panel”. It might be possible to share a ground grid but typically since it’s a separate system that includes ground rods. I haven’t tried to research sharing ground rods but unless you were very careful about for instance ground wiring sizes you are probably asking for a Code violation somewhere. I try to avoid this situation in installations because even if it’s legal you get into grounding issues. Look at the Steel Tube Institute technical articles where they get into issues that happen with long runs and poor grounding.

 

[art]

Thanks again!

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