radioactive cell and the conduit bends we have to work with

[Dyer-lectric]

Greetings all,

New engineer here, we are repurposing a waste storage facility from the 70's, and the cell we need to get our electronics in to have penetration's with a minimum of 5 bends (450 degrees). Specifically, the conduit I am working with is a 1" RMC with approximately 450 degrees of bend. Well, according to NEC 344.26, our max allowable is 360 degrees. Obviously that math doesn't check out. The crux of the issue is that due to shine (neutron and gamma radiation blasts), we cannot reduce the number of bends.

Does the NEC allow for exceptions in this?
Is it all up to my AHJ to give it the ol' "go for it!"
Or is there another process to pass an NEC inspection for older facilities with similar issues?

I appreciate any help given.

 

[tom baker]

No exceptions in the NEC
Your local AHJ may be understanding and allow you to go over 360.
In WA you can submit a form ($) and ask for a variance.
I have been told that you are paying for a no. but it seems like this is a special case. The 360 is based on pulling force going around bends and perhaps if you are pulling a small cable you could do some calcs on pulling tension, and demonstrate the cable won't be damaged.

 

[steve66]

I'm just wondering how your "electronics" are going to survive more than a few minutes in those conditions?

 

[roger]

There is 90.4

 

[xformer]

lead covered conduit?

 

[Dyer-lectric]

I'm just wondering how your "electronics" are going to survive more than a few minutes in those conditions?

Lots of shielding, and we're keeping all solid state devices out of the cell.

 

[Dyer-lectric]

lead covered conduit?

Yes

No exceptions in the NEC
Your local AHJ may be understanding and allow you to go over 360.
In WA you can submit a form ($) and ask for a variance.
I have been told that you are paying for a no. but it seems like this is a special case. The 360 is based on pulling force going around bends and perhaps if you are pulling a small cable you could do some calcs on pulling tension, and demonstrate the cable won't be damaged.

That would be unfortunate, but at least it is a step forward. (Hello from Hanford!)

 

[Dyer-lectric]

There is 90.4

That is the route that comes with the least amount of headache for me, thank you. So easy to lose track of earlier parts of the NEC when sifting through the behemoth.

 

[LarryFine]

The crux of the issue is that due to shine (neutron and gamma radiation blasts), we cannot reduce the number of bends.

Would a C-condulet be permissible? If so, you could have even more bends.

 

[BillyMac59]

No way to put a pullbox of some type in the run? The 360' is max bend between pull points...

 

[Dyer-lectric]

No way to put a pullbox of some type in the run? The 360' is max bend between pull points...

Not without compromising the safety of all involved, like roger stated above, I think our AHJ needs to determine if this can be an exception. Because without it, there could be no work, and that is not an option.

 

[tom baker]

Yes

That would be unfortunate, but at least it is a step forward. (Hello from Hanford!)

Off topic, I am ex navy nuke, got a tour of the Hanford B plant, fascinating look at how reactor control was done with electro mechanical equipment.

 

[steve66]

It probably goes without saying, but the 360 degree bend limit is probably based on standard conduit sizing, and standard bend radius.

So if you do go with 450 degrees of bends, make those conduits larger than the minimum size, and use long radius elbows.

 

[BillyMac59]

Can't speak for the NEC, but the Canadian (CEC) rule 12-942 states 360' of bend - including offsets - between pull points. Oversizing pipe and/or increasing bend radius is not part of the decision. As others have stated, the AHJ may give you a "one off" based on your application.

 

[don_resqcapt19]

There is no real reason we have a 360° fit-all rule. There are lots of cases where you can pull through double that without damage to the conductors. It is just that to have a requirement that specifies pulling calculations would be too difficult to work with.

As long as you do the calculations to show that the pulling tension and sidewall pressure won't damage the conductors or cables, being installed, I would write a 90.4 permission.

 

[synchro]

It's possible that the number of bends, conduit diameter, and bend radius were engineered to get sufficient attenuation of the neutrons and gamma rays that can propagate through the conduit and scatter as they hit the corners. So there may be constraints in place beyond just the electrical ones.

 

[ramsy]

The crux of the issue is that due to shine (neutron and gamma radiation blasts), we cannot reduce the number of bends.

It's possible that the number of bends, conduit diameter, and bend radius were engineered to get sufficient attenuation of the neutrons and gamma rays that can propagate through the conduit and scatter as they hit the corners. So there may be constraints in place beyond just the electrical ones.

Thanks to synchro for clarifying radioactive "shine". This raises a few points for me.

1) Who's the AHJ for wiring this hazard on Federal property?

While similar wiring methods & wire-pull calcs may be referenced, the AHJ for wiring this building may include the United States Nuclear Regulatory Commission (USNRC), among other Federal agencies.
www.nrc.gov/reactors/new-reactors/regs-guides-comm.html

2) Does the NEC apply?

NFPA-70 Scope most likely stops outside at utility services, per 90.2(C), even though X-Ray installations & equipment, which may utilize Gamma rays, in NEC 517 & 660 reference some authority in the Informational Notes.

517.70
Informational Note No. 2: In addition, information on radiation protection by the National Council on Radiation Protection and Measurements is published as Reports of the National Council on Radiation Protection and Measurement. These reports are obtainable from NCRP Publications, P.O. Box 30175, Washington, DC 20014

660.1
Informational Note No. 2: In addition, information on radiation protection by the National Council on Radiation Protection and Measurements is published as Reports of the National Council on Radiation Protection and Measurement. These reports can be obtained from NCRP Publications, 7910 Woodmont Ave., Suite 1016, Bethesda, MD 20814.

3) What raceways or wiring methods are tested for radiation?

NFPA-70 Special Occupies in Chapter 5 do include Hazardous (Classified) locations, based on flammable ratings of fuels & gases, and typically include "Explosion Proof" and Mineral-Insulated raceways, but the NRTL listing agencies may not necessarily investigate radiation testing, except for UL White Book categories for microwave appliance radiation emission, and prohibiting Ionization detectors in radioactive environments.

UL White Book
INSPECTION AND MEASURING ELECTRICAL EQUIPMENT, SPECIAL INSPECTION EQUIPMENT (NYQD)

FACTORS NOT INVESTIGATED
These products generate radiation or contain radioactive materials or involve working with toxic materials, or other potentially harmful technologies, where data regarding levels of exposure and physiological effects are not investigated. The accuracy of measured, analyzed or prepared quantities has not been investigated.

My guess is wire insulation more durable than XHWN-2, or specific for Gamma radiation could be specified, with unique wire-pull calcs.

If radiation testing exists for wiring methods & raceways, manufacturer data, federal regulations, or DOD reactor applications may be better resources.

 

[Hv&Lv]

The 360 degree rule is a bad metric for doing away with sidewall and pulling tension calculations.
There are many cases where an electrician can set up an NEC legal pull and damage the cable.
There are also cases where the same electrician can set up a pull with 720 degrees of bends and not damage or struggle pulling this wire in.

Engineering supervision should take over in certain cases.
The NESC spells it out better…
341.A.2 Pulling tensions and sidewall pressures on the supply cable should be limited to avoid damage. Note; Manufacturers' recommendations may be used as a guide.

 

[LarryFine]

If the extra elbows is part of this requirement, then it has been done before. Find out how it was accepted.

 

[Tulsa Electrician]

I recently seen a job were they had over 630 with out a pull point.
One crew said there under 360. The other said the same. One outside equipment room and the other inside. So each crew said there compliant. Basically each did not want to do any extra work. Said it was the others fault.
Then the wire pulling guys were like not my job.
The end result was a lot of damaged wire that would not meg out. Some did and some did not.
The long radius idea is a good one along with good installation practice will make the difference. A good pipe runner is a must in your case.