Grounding Autotransformer Overcurrent Protection

[beanland]

2011 NEC 450.5(B)(2)(b) requires overcurrent protection for a grounding transformer at 125% of rating but specifically states that delay of tripping for proper function is allowed. This means that a thermal or overload element is required but that neither a short-time nor instantaneous (magnetic) element is required. I am looking for a molded case 480V 3-phase circuit breaker that has a thermal element but no magnetic element or, if electronic, has neither short-time nor instantaneous elements. I am totally unable to find anything. Square D even has a FAQ that states they do not offer any thermal-only circuit breakers.

In the utility industry, working with high-voltage breakers, we often have time delayed only elements, but the equipment is $1000's.

I need a 100A 480V 3-pole thermal-only breaker.

Does any one know of a manufacturer?

 

[iceworm]

I need a 100A 480V 3-pole thermal-only breaker.

Does any one know of a manufacturer?

No. All of the CBs that I have seen, in that frame size have an inherent instantaneous trip. In fact, all of the molded case CBs of any frame size (that I have seen) have an inherent instantaneous trip.

As I recall, there are hi instantaneous trip CBs listed in the catalogs. Perhaps one of those is high enough to be out of the way

iceworm

 

[zog]

2011 NEC 450.5(B)(2)(b) requires overcurrent protection for a grounding transformer at 125% of rating but specifically states that delay of tripping for proper function is allowed. This means that a thermal or overload element is required but that neither a short-time nor instantaneous (magnetic) element is required. I am looking for a molded case 480V 3-phase circuit breaker that has a thermal element but no magnetic element or, if electronic, has neither short-time nor instantaneous elements. I am totally unable to find anything. Square D even has a FAQ that states they do not offer any thermal-only circuit breakers.

In the utility industry, working with high-voltage breakers, we often have time delayed only elements, but the equipment is $1000's.

I need a 100A 480V 3-pole thermal-only breaker.

Does any one know of a manufacturer?

No such animal exists

 

[ron]

I've seen power (SWGR listed to UL-1066) circuit breakers that have an instantaneous element that can be disabled, but we are feeding 30 cycle rated equipment for those applications.