X-Ray Machine Feeder Conductor

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fairelectric

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Have a used X-Ray machine that is rated for a 100 amp disconnect means. Service to disconnect conductor is 4 conductor #2 SER Aluminum cable(2,2,2,4). X-Ray installation people(third party) came to install today and said these conductors must be copper. There were no installation details on conducter material, only ampacities. Is there an article in the code that specifies this or is it manufacture specific? Any help would be appreciated.

Thanks,
Shannon Faircloth
 
Re: X-Ray Machine Feeder Conductor

Shannon,
First Of All #2 SER Aluminum Does Not Get You To 100A At The 75 Degree C Column In Table 310-16 #2 Aluminum Is Good For 90A.
Secondly The X-Ray Equipment May Have Specific Requirements For The Type Of Conductors To Be Used To Feed It This Information Should Be In The Equipment Manufacturers Product Literature. This Will Not Be An NEC Issue. I Know With Square D Isolation Panels In Hospitals They Spell Out The Manufacturer Of The Cable That You Are To Use To Feed Their Equipment. This Gets Into Warranty Issues.
-Ed
 
Re: X-Ray Machine Feeder Conductor

I can't imagine a reason that AL wiring would not be permitted or not desired from the service to the disconnecting means. I can understand if the connection to the X-ray equipment itself called for that specification, but not the feeder wiring.

I agree that #2 AL is not rated for 100A, but a 100A disconnecting means can still be used.
 
Re: X-Ray Machine Feeder Conductor

The installation people may be worried about voltage drop. I would assume it would be higher for alumnium than copper with a similar ampacity.

Steve
 
Re: X-Ray Machine Feeder Conductor

Voltage drop would be nearly identical at this load using either AL or CU.

Assuming a 100A single phase load and an example distance of 50', the voltage drop with #1 AL 100A conductors = 2.53V. the VD of #3 CU 100A conductors = 2.45V. A difference of only .08V.
 
Re: X-Ray Machine Feeder Conductor

This is common of xray people and manufacturers.

They'll tell you you've got to give them oversized wire, oversized conduit, have the room spotless, send their mother flowers, send their father flowers, and a whole lot of other things, then when you ask them why, they'll give you a definite "because".

If you try to arrange an appointment to talk to one of their (ahem) engineers, you'll get a salesman or an installer who will reinforce the answer of "because".

I have a set of Cath Lab prints we are doing now that says; Phase to Phase impedance @ 440v can be no more than .038W. Can anybody tell me how impedance is measured in power verses ohms?

I had another (big name) manufacturer require (5) 1/0 conductors to a unit in an existing facility that would mean opening walls (infection control issues) to install a larger conduit when the max load was 60 amps.

They finally allowed #1's which would fit into the existing conduit. When we were done with the pull to the disconnect, we asked where they wanted the line side conductors to go and they said they wanted the three phases and EGC to go their trough, we asked what the neutral was going to do, and they said it wasn't used.

I asked, "then why did it have to be run and almost cause this facility to spend mega bucks to open up walls and ceilings to run a new conduit to accommodate the 1/0's that was ovesized in the first place" and their answer was in essence "because". :roll:

Roger

[ July 21, 2004, 09:12 PM: Message edited by: roger ]
 
Re: X-Ray Machine Feeder Conductor

Thanks everyone for the great feedback. You are correct on the ampacity of 90 amps. I forgot to add that along with the stated 100 amp disconnect the unit has a full load amperage rating of 70 amps. Guess I will meet with them again this morning and see what unravels. Let you guys know.

Thanks Again,
Shannon
 
Re: X-Ray Machine Feeder Conductor

We are installing 2 new X-Ray machines on our campus (Austin Peay State University) and also recieved wiring data that was "illogical". The factory engineer stated that altho a 100 amp disconnect is required, the larger spec on the wire size (#00AWG) is to accomodate the 190 amp surge during the 'X-Ray' activity (lasting upto several seconds) and prevent any voltage drop during the event. Since we are over 200 feet in wire length from the source panel, we have arranged to install 37.5kVA transformers to step down 480 VAC to 120/240VAC singlephase and required to use #00AWG wire to feed it. 'Voltage drop' is the buzz word used. DOes this help? (probably not).
 
Re: X-Ray Machine Feeder Conductor

Yes, that makes sense however them specifying the size of the conductors arbitrarily does not. The VD they are talking about depends on the length of the conductors as well as what they are fed from and maybe even the utility in some cases. Each installation should be engineered according to the specifics.

-Hal
 
Re: X-Ray Machine Feeder Conductor

as long as you installed what the specs required then your off the hook.If they want to now specify copper then that is a change and requires a PO
 
Re: X-Ray Machine Feeder Conductor

Jim,
Originally posted by jimwalker:
as long as you installed what the specs required then your off the hook.If they want to now specify copper then that is a change and requires a PO
Click to expand...
unfortunatly, as a blanket statement this is not true.

Most (all that I'm aware of) contract documents will specify somewhere that you (EC) are responsible for all local, NEC, and applicable codes, and if this changes the specs it is still part of the "Intent" of the signed contract. This is where ignoring in depth review of the contract documents can make or break a job.

Another part of this is the fact that if you do substitute a submittal item, (say a Lithonia fixture verses a Halophane) and the submittals are approved, it does not necessarily mean the material is acceptable. Just because you as the contractor review and stamp them, then send them down the line and they come back stamped approved by all others, does not relieve you of providing the quality of material "intended" which may not be the approved item/s.

"Intent" can legally override stamped (and even signed) papers.

If an EC knew the material may be border line and did not red flag any deficiency, this EC can be responsible for replacing the material including labor and expenses.

Not notifying a designer of known "errors or omissions" will be another thread someday. ;)


BTW, did you mean C.O. (as in Change Order) in lieu of P.O.

Roger

[ July 23, 2004, 10:05 PM: Message edited by: roger ]
 
Re: X-Ray Machine Feeder Conductor

...Most (all that I'm aware of) contract documents will specify somewhere that you (EC) are responsible for all local, NEC, and applicable codes, and if this changes the specs it is still part of the "Intent" of the signed contract.

Unfortunately this fact is widely misunderstood. Some time ago I started a thread about an EC refusing to provide an equipment ground conductor to the telecom room. He said it wasn't in the drawings or specs. Point of my posting was that I maintained that it was an NEC requirement and he was required to provide it per the above clause in his contract regardless of whether it was specifically indicated on any drawings or specs. Most here disagreed...

-Hal
 
Re: X-Ray Machine Feeder Conductor

The VD they are talking about depends on the length of the conductors
Click to expand...
Most X-ray equipment I have seen has a table for the feeder size. Length vs. wire size. For example, 1/0 for 0-50', 2/0 for 50-100', 3/0 for 150-200'.....

On the other hand, many xray units are relocated, and the manufacturer is out of business. Then, you just have to take the xray installer's word for what is required.

Steve
 
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