Two 200A X Ray Circuits via 400A safety Switch

[matthewswain]

I want to feed two 200A x ray circuits directly from a 400A Siemens safety switch that has double lug for line and load. This is not a service or tap. I want to know if I can run two 200A circuits in parallel via one 400A circuit through the safety switch. The line is one 600kcmil circuit (via transformer) with two 250kcmil (for voltage drop x ray). All I can find in NEC atm is 240.8 statimg equipment needs to be listed. Siemens spec sheet does not specify but has double lug. I am concerned that the AHJ may consider this a tap. Can I run two 200A circuits in parallel from a 400A switch without installing two 200A disconnects within 10'

 

[matthewswain]

200A shunt trip breaker panels at end of feeder circuits as disconnecting means for x ray

 

[tom baker]

You say you are not doing a tap, what is the ampacity of the 400 amp load side wires?

 

[roger]

If the conductors are not landed together at both ends they are not in parallel, you are describing taps.

 

[ptonsparky]

Sounds like a Tap to me.
Try 240.21(B)(2)

 

[kwired]

I want to feed two 200A x ray circuits directly from a 400A Siemens safety switch that has double lug for line and load. This is not a service or tap. I want to know if I can run two 200A circuits in parallel via one 400A circuit through the safety switch. The line is one 600kcmil circuit (via transformer) with two 250kcmil (for voltage drop x ray). All I can find in NEC atm is 240.8 statimg equipment needs to be listed. Siemens spec sheet does not specify but has double lug. I am concerned that the AHJ may consider this a tap. Can I run two 200A circuits in parallel from a 400A switch without installing two 200A disconnects within 10'

Are you feeding two individual pieces of equipment or are you landing both sets of conductors at the same equipment?

If conductors are joined at both ends to effectively make one larger conductor that is basically the definition of a parallel conductor, you treat it as though it were one larger conductor, so in this case it would effectively be same thing as if you ran a 500 kcmil conductor and would have an ampacity of (255 x 2) 510 amps and would be ok to protect at 400 amps.

If this is supplying two different pieces of equipment then the conductors are not in parallel and the conductors are only 255 amps each run and would need overcurrent protection according to that ampacity - next size up rule can apply so 300 amps device would be permitted but load still needs to be no more than conductor ampacity of 255.

You could make a feeder tap if you meet the conditions of feeder tap rules in 240.21 but your description here sounds like probably has too much length to meet any those rules other than if it were an outside tap. Said taps if allowed do need to have proper overcurrent protection at load end of the tap.

The listing requirement in 240.8 is about fuses or breakers used in parallel to one another not conductors so doesn't apply to anything you have described. The dual lugs in your 400 amp Safety switch is mostly about accommodating use of parallel conductors for said switch, though it very well can easily have two feeder taps connected to the load side simply because of convenience of how it works out.

 

[roger]

Are you feeding two individual pieces of equipment or are you landing both sets of conductors at the same equipment?

The first sentence of the OP
"I want to feed two 200A x ray circuits directly from a 400A Siemens safety switch that has double lug for line and load. "

 

[kwired]

The first sentence of the OP
"I want to feed two 200A x ray circuits directly from a 400A Siemens safety switch that has double lug for line and load. "

Trying to determine if terminology or use of it is contributing to the question here or not. As worded yes he has feeder taps to two pieces of equipment.

If the equipment doesn't have overcurrent protection at or within they are improper feeder taps - ignoring length restrictions of the taps or if they happen to be outdoor taps which have no length restrictions.

 

[petersonra]

The first sentence of the OP
"I want to feed two 200A x ray circuits directly from a 400A Siemens safety switch that has double lug for line and load. "

Pretty much has to be tap conductors and thus have to follow the tap rules, despite the OP stating it is not a tap.

 

[roger]

As worded yes he has feeder taps to two pieces of equipment.

And unless he comes back and says otherwise we need to go with what he said. Muddying the waters leads nowhere.

 

[matthewswain]

Thank you for the responses. I appreciate it. Yes, there are two 200A shunt trip breakers servicing two separate x ray machines at load side. Obviously this is considered a tap, wishful thinking on my part perhaps.

 

[kwired]

And unless he comes back and says otherwise we need to go with what he said. Muddying the waters leads nowhere.

I did start that post with a question that basically was asking him to clarify whether he was feeding two individual pieces of equipment then proceeded to explain, or at least attempted to, what may or may not be correct. With more explanation he could bring up details that he never mentioned in OP and end up turning the common portion of this into legitimate feeder, like say they do tie together in a splice box then has taps to the two pieces of equipment that do comply with tap rules.

 

[ptonsparky]

I did start that post with a question that basically was asking him to clarify whether he was feeding two individual pieces of equipment then proceeded to explain, or at least attempted to, what may or may not be correct. With more explanation he could bring up details that he never mentioned in OP and end up turning the common portion of this into legitimate feeder, like say they do tie together in a splice box then has taps to the two pieces of equipment that do comply with tap rules.

Yes, those disconnects could be 50 of wire apart if he chooses the correct tap rule. He needs to play the game by the rules.