cutting a conduit without severing wiring inside it

[malachi constant]

Hi all,

I am designing a lighting retrofit where the Owner requests a one-for-one replacement of highbay lights. The lights are currently hard-wired, and the Owner wants the new lights to be connected via cord and plug. There are a few hundred fixtures and downtime (plus other costs) needs to be limited. The hardest part to factor is the conduits disappear up into a fabric insulation ceiling which presents two problems. One, the insulation may or may not be hiding junction boxes. And two, it is difficult (impossible) to visually trace conduits to see what goes to where. I'm concerned that we will need to cut the conduits a few feet short to allow the outlet box to be installed, but in cutting the conduit short we will sever the wire within it. It will be hard to pull back wire given the conditions.

I tentatively proposed a solution that sounds viable but I've never heard it done before: use something like a pipe-cutter (like used on copper plumbing pipes) to cut two feet off the EMT without damaging the wires within. Drop off the two feet and slide a box over the end. Is this something that is done? The maintenance folks thought it was a slam dunk idea but before I sent it out for public bid I figure I better make sure it is a viable option.

I'm guessing I'll hear other solutions from the community, so will add a little more information. Most of the fixtures already have a cord and plug, we're talking about maybe 15% of the fixtures. We'd like to keep them all in the same location at the same height - it's a nice existing grid that lines up with a number of other systems, limiting the ability to move things over or drop the heights. It's a high-profile event space, with some arena seating that will keep some spectators near eye level with the lighting, bolstering the need to keep it looking clean and neat. All that to say it would be really nice to cut the conduit a couple feet short without severing the wire.

Let me know your thoughts. Thanks!

 

[malachi constant]

Ooh, I have another somewhat related question! A few fixtures being added that are RGB DMX color-changing type high-bay floods. These are brand new locations, so we will be adding conduit to these locations. These will require 0-10V control wiring to them. The Owner wants the fixtures to be cord and plug for quick disconnect. Easy for the line voltage wiring, but what about the control wiring? I was thinking an SO cord from the fixture to a junction box (or the j-box to the fixture body), and then have the wires connected with a quick-disconnect. But in this scenario once you disconnect them, that SO cord is still connected to the j-box (or fixture body) and would need the connector unscrewed to allow the fixture to be taken down. My concern would be you could drop the connector while you are up in the bucket - that's not the end of the world, but we're trying to simplify maintenance here. All that to say, what is the simplest way you can think of to legally connect and disconnect control wiring to a luminaire?

 

[infinity]

Can you slide a smaller diameter piece of EMT or RMC into the existing raceway to protect the conductors while cutting? You should be able to cut around the EMT.

 

[junkhound]

I once cut 2 feet out of a 2" rigid service entrance conduit (200 A service from 50 kVA xfmr) with power ON. POCO could not accommodate my schedule due to big storm. (needed to lower weatherhead due to nearby storm damage)

Took off the weatherhead, slld down the drip loop out of the way, then slid split sections of pvc pipe into the conduit.

Cut circumference around 2 ft from end, then full length cut down both sides and removed the 2" rigid sections. You wont even have to do the long side cuts or split the 1-1/2" pvc if it a a straight section yu are cutting off. I used an angle grinder with thin diamond blade and depth stop. Slid the weather-head back onto the conduit after filing out the slight ridge edge.

OP's pipe cutter should work well in his situarion, esp if a ferrule added to protect the pipe cutter ridge left, or if a reamer with hollow center can be found to remove the ridge. .

 

[electrofelon]

I think the pipe cutter would work. Never tried one on EMT though. I am just concerned as they tend to leave a burr on the inside of the tubing. Perhaps one of these deburring tools would clean it up:

 

[LarryFine]

You also may be able to push 6" of wire into the conduit, cut the conduit, and then pull the wire back out after cutting.

 

[kwired]

Problem with tubing cutter is it leaves a very sharp edge that easily will cut right into THHN/THWN conductor insulation. This isn't as easy to "deburr" as a copper tube is either, and having conductors in the way makes it even more difficult. Didn't say it is impossible, but not any fun.

 

[Coppersmith]

I have used a tubing cutter on EMT before and it does work, but leaves a burr inside the pipe which will cut into the insulation if not removed. A rat tail file can be used to remove the burr, but it's slow going. I would hate to have to do a couple hundred of them.

 

[mopowr steve]

I’ve cut EMT a number of times doing what your proposing with a tubing cutter then very carefully debur the inside with my knife or file so not to damage the conductors. Just take your time.

 

[tom baker]

I have done this by using a short length of smaller dia conduit/pipe and slide into the pipe being cut off with the wires inside it. I used a sawzall, with a file to deburr, as it was 2" conduit.
Do a mock up on a bench to work out your method.

 

[tkb]

If you score the emt with a tubing cutter, it will snap if you bend it at the cut.
There is a ridge, but it is not sharp because the cutter did not cut all the way through.

 

[JoeyD74]

I’ve used a tubing cutter for EMT and the trick I found was not to cut the pipe all the waythrough and then snap the piece off. It eaves a much smaller and not usually sharp edge.

 

[electrofelon]

I have used a tubing cutter on EMT before and it does work, but leaves a burr inside the pipe which will cut into the insulation if not removed. A rat tail file can be used to remove the burr, but it's slow going. I would hate to have to do a couple hundred of them.

I’ve cut EMT a number of times doing what your proposing with a tubing cutter then very carefully debur the inside with my knife or file so not to damage the conductors. Just take your time.

Try one of those deburring tools if you havent. They are slick.

 

[Cow]

I'm concerned that we will need to cut the conduits a few feet short to allow the outlet box to be installed, but in cutting the conduit short we will sever the wire within it.

How will the box be supported?

 

[malachi constant]

Great info everyone!
It is a public bid job so I will make it crystal clear in the contract documents what the situation is, and what the recommended solution is, while allowing for contractors to pursue other methods. Recommended solution will be:
1. Insert a smaller diameter pipe into the EMT to protect the wiring
2. Cut the EMT by either using a tubing cutter to cut it all the way through, then deburr; OR score the EMT partially through and then snap off (to avoid leaving a sharp ridge).
3. Install box and outlet, providing strut as necessary to secure box.

Thanks!

 

[DBoone]

Can you slide a smaller diameter piece of EMT or RMC into the existing raceway to protect the conductors while cutting? You should be able to cut around the EMT.

Great idea

 

[tom baker]

What about a Klien Electricans Tubing Scoring Tool, scores and than emt is snapped
https://www.homedepot.com/p/Klein-Tools-Electrician-s-Conduit-Scoring-Tool-88906/100662410

 

[Fulthrotl]

How will the box be supported?

by using a condulet instead?

 

[winnie]

In terms of cutting EMT I am not a professional; but in my DIY experience the 'score and snap' approach works pretty well. Sometimes it leaves a burr and sometimes it does not.

My biggest concern here is deburring the cut with conductors in place. Is there a bushing made for emt similar to the 'red heads' used for AC cable?

Regarding 'cord and plug' connection for the control lines; there are loads of connRegarding the 0-10V control lines being 'plugged in' there are loads of low voltage connectors available. It looks like 'XLR' connectors are pretty common for DMR lighting. My understanding is that the control lines should be separated from the power lines, so I don't think the low voltage connector can be in the same JB as the power connector.

-Jon

 

[Strathead]

Try one of those deburring tools if you havent. They are slick.

I have both, used a tubing cutter, and one of those deburring tools. Usually the lip that is left is too much for the deburring tools to remove, honestly, at least. For Tom Baker, IMO the Klein scoring tools is really just a pipe cutter marketed under a different name. Using a sharp blade on a tubing cutter and using more revolutions in lieu of more pressure will reduce the lip. then I have still only found a rat tail file effective at removing the burr. I much more ideal way to do this work is to tie a string to the wires, pull them back and use a blade to cut the conduit. Still trying to prevent cutting the string, but if you do, it will just take some work to get it back out. One other thing I have done. Score it with a pipe cutter and then carefully cut around with a hack saw. Also, if you are putting a junction box on the end, the pipe can be cut about ten inches from the end first, since all you will need is 8 inches of wire when you are done.

From a specifying angle, and I am an estimator. I Would greatly appreciate you identifying the problems, but not the solution. Let me decide how to do it. Methods may change depending on the situation.