X-Ray Equipment

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AZJeff2013

AZJeff2013

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Marion, Illinois
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Electrical Design / RCDD
Can someone please explain X-Ray equipment as it relates to NEC load calcs. Years ago I worked for an engineer that did not enter wattage into the panel schedule, only breaker and wire sizes. The reason being due to the load being so momentary. I just spoke with a Caterpiller generator rep who basically said the same thing regarding the software they use to size generators. He doesn't ever recall entering X-Ray load into the sizing software on the multitude of healthcare jobs he as been involved with. Can someone either confirm this or set me straight...I am currently designing a veterinary clinic and have been instructed to add the X-Ray to the generator if it won't "cost to much" as it relates to final generator size.

Thanks!

Jeff
 
Brief Load

Brief Load

I worked on a clinic with an x-ray a few years ago. The thing is that given how brief x-ray load is, it does not count toward continuous loading; nothing ever has time to warm up. BUT, the generator must still be able to support it and the breaker must not trip. So, even if the x-ray load does not count in the load calculations, it needs to be considered in the generator loading.
 
beanland said:
I worked on a clinic with an x-ray a few years ago. The thing is that given how brief x-ray load is, it does not count toward continuous loading; nothing ever has time to warm up. BUT, the generator must still be able to support it and the breaker must not trip. So, even if the x-ray load does not count in the load calculations, it needs to be considered in the generator loading.
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What is "brief" instantaneous used to be defined as 5 cycles or less on a nuclear submarine. Prior to the electronic trip unit days. The trip setting for instantaneous trip for and inverse time circuit breaker is generally 10 times the breaker rating. So. if your breaker trips you likely have other problems.
 
I can confirm that a medical x-ray machine runs only briefly, but quite a bit slower than "instantaneous". If memory serves me, something in the neighborhood of 1 to 10 seconds per image.
But when it's running, it will consume several kW. (if it's a small-animal clinic)

To be certain the generator can handle it, you could interlock it with an interruptable load such as the air conditioner or water heater.
 
beanland said:
I worked on a clinic with an x-ray a few years ago. The thing is that given how brief x-ray load is, it does not count toward continuous loading; nothing ever has time to warm up. BUT, the generator must still be able to support it and the breaker must not trip. So, even if the x-ray load does not count in the load calculations, it needs to be considered in the generator loading.
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The x-ray equipment may have specifications on how much voltage drop is allowed during the short time it does draw peak current, which is likely more critical than kVA rating of the source.
 
drcampbell said:
I can confirm that a medical x-ray machine runs only briefly, but quite a bit slower than "instantaneous". If memory serves me, something in the neighborhood of 1 to 10 seconds per image.
But when it's running, it will consume several kW. (if it's a small-animal clinic)

To be certain the generator can handle it, you could interlock it with an interruptable load such as the air conditioner or water heater.
Click to expand...

One second isn't briefly in electrical terms. I know you aren't saying it is, so this isn't directed at you, just referencing your information.
 
Strathead said:
One second isn't briefly in electrical terms. I know you aren't saying it is, so this isn't directed at you, just referencing your information.
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It is far from being a continuous load though.

Motor driving a high inertia load - 1 second of acceleration time isn't necessarily a long time either even though current may be pretty high at this time compared to what it is at running speed.
 
Load calculations for xray equipment is right in 517.

I believe its 50% of the momentary rating for the 1st xray.

Its very clear.

Edit: Opps - I just realized you said its for a vet. So technically 517 may not apply.

However, it would seem prudent to use the same load calculations as for a medical office since the equipment is so similar, and would have a similar 'On" duration.
 
steve66 said:
Load calculations for xray equipment is right in 517.

I believe its 50% of the momentary rating for the 1st xray.

Its very clear.

Edit: Opps - I just realized you said its for a vet. So technically 517 may not apply.

However, it would seem prudent to use the same load calculations as for a medical office since the equipment is so similar, and would have a similar 'On" duration.
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Art 660 has the same requirements but then again it says "non medical use"
 
I'm assuming there's a separate section for industrial X-rays-- metal pieces, etc.
 
hbiss said:
With respect to x-ray I would think a veterinary use is medical. I wouldn't think using HCF cable for the exam rooms though would be required.

-Hal
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Though maybe not a bad idea not required, read first sentence of 517.1. 517 doesn't apply to veterinary care.
 
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