Voltmeter Protection

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The circuit is a high current transformer (60V at 2700A).
I wanted protection based on any meter failure/shorts? Not necessary?
 
NetNathan said:
The circuit is a high current transformer (60V at 2700A).
I wanted protection based on any meter failure/shorts? Not necessary?
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good question. Its not a branch circuit so it doesn't need branch circuit protection. Not sure the AIC rating of the supplemental breaker you want to use is adequate for the available short circuit current you have though.
 
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petersonra said:
good question. Its not a branch circuit so it doesn't need branch circuit protection. Not sure the AIC rating of the supplemental breaker you want to use is adequate for the available short circuit current you have though.
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These breakers have a 10KA AIC and the price is right, too:

https://www.automationdirect.com/ad..._(0.5A-40A,_FAZ-CXX-1-NA-SP)/FAZ-C0P5-1-NA-SP

I'd probably consider a two-pole breaker, if your transformer output is ungrounded.


ScenreryDriver
 
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BTW, where are you getting your transformers from? I have a project coming up potentially in the 800 - 1200 A range. I have been having trouble finding alternate suppliers for low voltage, high current type xfmrs. Are you having to get them custom made?
 
petersonra said:
BTW, where are you getting your transformers from? I have a project coming up potentially in the 800 - 1200 A range. I have been having trouble finding alternate suppliers for low voltage, high current type xfmrs. Are you having to get them custom made?
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The transformer I am using is custom built by Hunterdon Transformer in Alpha, NJ. It is a "Variable Reactance Transformer" (VRT) which has a DC winding in between the primary and secondary. The amount of DC current applied is what controls the 0-60 Volt output of the VRT secondary.
It is a slick design that is current limiting on the output, if you direct short it it goes to max voltage and very low current. This gets me around having to fuse the secondary (Can you imagine the size of a 3000A fuse?).
It is used for low resistance heating elements in a vacuum furnace (Now you get into NFPA-86D). Total resistance of the secondary circuit is around 1 ohm.
We usually use 3 single phase transformers in a Delta primary. This way I can independently control each of the 3 heating zones in the furnace. The PID controls the DC voltage to the DC winding.
 
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