Isolation transfomer secondary neutral bonding

[llhilger]

I called technical support for a certain brand of 15kv isolation transformer single phase 240x240 asking for clarification on bonding the neutral on the secondary side to ground. The response I received was you don't have too but you can if you want. My engineer told me I should bond it with ground. Any clarification on this as I do not understand why the manufacturer technical support would say this.

 

[texie]

I called technical support for a certain brand of 15kv isolation transformer single phase 240x240 asking for clarification on bonding the neutral on the secondary side to ground. The response I received was you don't have too but you can if you want. My engineer told me I should bond it with ground. Any clarification on this as I do not understand why the manufacturer technical support would say this.

You mention 240 X 240 volts but in the same sentence you say you have a neutral. Does the secondary actually have a center tap? Does the load need to be connected to a grounded system? These details will change the answer. For example, if you only have 240 on the secondary you could run it ungrounded but that will trigger other requirements. In general unless you specifically need an ungrounded system it is usually not good idea.

 

[ramsy]

If inside the building, under NFPA–70, book smart people using definitions under article 100, may be providing answers by the book.

Ground = Neutral = White

Grounding/Bonding = Earth = Green

If outside the building, or Utility side, consult the NESC for definitions of Ground.

 

[infinity]

If inside the building, under NFPA–70, book smart people using definitions under article 100, may be providing answers by the book.

Ground = Neutral = White

Grounding/Bonding = Earth = Green

I think that you meant grounded.

 

[llhilger]

Sorry Yes it is requiring a grounded conductor on the secondary. Picture is what tech sent and said X2 and X3 could be connected to the grounding conductor that feeds the 240/120 single phase panel or not be connected.

 

[Andy Delle]

I think if it's not a grounded centertap 120-0-120 configuration, one of the 240v ends must be grounded. Otherwise how will ground to hot (or either wire) short trip the OCPD? It's no different that a 120v circuit. There must be a bond between the "neutral" side and ground. In the rare case of a 240 single phase secondary lacking the 120v centertap, then one side of the transformer winding is essentially the new "neutral".

Unless I'm mistaken this is how European single phase 240v is done. One leg is grounded just as we do with our neutral.

As sated above in special applications you can run un-grounded but that triggers other strict code segments, the minimum I think would be GFCI.