Protection from physical damage DLO/RHW-2 conductors.

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74glencoe

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Alamogordo NM
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Journeyman electrician
I have recently changed jobs and have ran onto some installations which use DLO conductors as feeders with "open" wiring as the method (no conduit, not part of a cable assembly, and no cable sheath). I can not find in the code where this is expressly prohibited or allowed. It simply seems to be dangerous to me as the conductor insulation is constructed to give the conductor a 2000 volt rating and not as a protection from damage. I have next to zero experience with DLO conductors and would appreciate some advice on the code compliance of this application.

They are also claiming that dlo conductors within an enclosure, passing through a knockout and laying directly on the earth are considered to be "in free air" and the ampacity should be based on 310.15(B)(17). I adamantly disagree, although free air has been undefined until the 2020 code cycle. I believe that a conductor in contact with dirt/rocks/sand or inside a disconnect or transfer switch is not free air, please correct me if I am wrong.

Thank you.
 
Just to be sure, is that really RHW-2 or another fine-stranded flexible type? If those are W or SC, then the ratings come from Art 400 and the insulation is only 600v but very robust.

If those are RHW-2, then I don't think laying them on the ground is compliant anyway, but many people do consider OTG as free air if the conductors aren't bunched or covered. (What's the application/conditions?)

(I really wish folks would stop saying "DLO" but that's probably a losing battle on my part.)
 
in one a
Just to be sure, is that really RHW-2 or another fine-stranded flexible type? If those are W or SC, then the ratings come from Art 400 and the insulation is only 600v but very robust.

If those are RHW-2, then I don't think laying them on the ground is compliant anyway, but many people do consider OTG as free air if the conductors aren't bunched or covered. (What's the application/conditions?)

(I really wish folks would stop saying "DLO" but that's probably a losing battle on my part.)
Application: 120/208 system, 400 amp disconnect feeding a 400 amp transfer switch. the transfer switch is also fed by a portable trailer mounted generator with 400 amp overcurrent protection, which in turn feeds a panel. all of the wiring is RHW-2 without conduit. the feeders are just draped out of the enclosures and over to the next enclosure. The feed from the generator is just laying on the ground waiting for someone with a clipboard to go walking through and trip over. It is the most hack thing I have ever seen in my entire career. The fine braid conductors are terminated in normal mechanical lugs, there is no abrasion protection in the knockouts, no cable clamps or connectors, and generally just looks like an abomination. I would post pictures but we are really not allowed to take photographs.

How can laying on the ground or within an enclosure be considered free air? free air to me is a cable strung between insulators with no more than 3in in 10ft in contact with insulators, as is my experience from high voltage work.

in one location they are rhw-2, in another it is welding cable/sc i believe.
with either is the insulation "robust" enough to be used as permanently installed without conduit/ cable sheath? if this is true please site an article or other source, thanks.
 
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Be careful....type W does not mean "welding cable"*; both W and SC are Art 400 portable cords and can be permanently installed in some circumstances. I'm harping on the exacy type because it's important.
*like "DLO", it's not a recognized type.

(is this a temp. setup or long-term/permanent? Makes a difference)

Even if it's Art 590 temporary....
Assuming that's really RHW2, it should be in some sort of protection (usually pipe/conduit).
Any conductor needs protection around a rough hole in metal, and ought to be strain-relieved anyway (for temp work, a piece of rope will do the job most of the time) and for a temp setup you don't necessarily need box connectors.
Conductors on the ground shouldn't run through traffic areas but could be protected by traffic cones or cable ramps.

Free-air? it's all about heat dissipation. If the conductors can radiate off any heat they generate without melting, I call it free-air (but I'm not the AHJ). It's very common in temp installations to lay cables on the ground and isn't an issue.

Please check Articles 400 and 590.
 
not a lot different than many temporary installations.
can you show me where it is allowed, even for a temporary installation? 590.4 (H).I know abrasion protection is required, and I know that the conductors need a listed mechanical lug or crimp connector, but I can not find where insulated conductors can be installed without a covering anywhere in the nec.
 
Be careful....type W does not mean "welding cable"*; both W and SC are Art 400 portable cords and can be permanently installed in some circumstances. I'm harping on the exacy type because it's important.
*like "DLO", it's not a recognized type.

(is this a temp. setup or long-term/permanent? Makes a difference)

Even if it's Art 590 temporary....
Assuming that's really RHW2, it should be in some sort of protection (usually pipe/conduit).
Any conductor needs protection around a rough hole in metal, and ought to be strain-relieved anyway (for temp work, a piece of rope will do the job most of the time) and for a temp setup you don't necessarily need box connectors.
Conductors on the ground shouldn't run through traffic areas but could be protected by traffic cones or cable ramps.

Free-air? it's all about heat dissipation. If the conductors can radiate off any heat they generate without melting, I call it free-air (but I'm not the AHJ). It's very common in temp installations to lay cables on the ground and isn't an issue.

Please check Articles 400 and 590.
This isn't a cable assembly, it is a single conductor. I have hooked up multiple carnival style temporary installations and conductors have always been part of a cable assembly such as SO, SJ, TC etc. or contained within a conduit of some type. I believe the biggest problem here is a complete lack of AHJ (federal installation). There is no inspector, no Engineering, and just about no workmanship.
 
Since it is a dual rated cable and the only rating that is permitted is the RHH rating and that makes the parent text in 310.10 apply. That requires the conductors to be installed in a Chapter 3 wiring method.

As far as the free air ampacity, even if it was permitted, you have an issue with the terminal ampacity rating rules in 110.14(C). The ampacity of the termination is limited to those found inTable 310.16, unless specifically marked for use with the ampacities from other tables.

As far as Article 590. 590.2(A) says that unless modified in 590, all of the other code rules apply. There is nothing that permits a single conductor of a type shown in 310.4 to be installed without being in a Chapter 3 wiring method.
 
Don's post just popped up- fully agree; that's why type is important- does 310 (R**) or 400 (W or SC) apply.

If the NEC doesn't prohibit something, it's generally allowed; only sometimes is a practice specifically allowed.

I've been referring to single conductors. I've done a lot of temporary setups using single conductors (always W or SC); they're almost never run in conduit*- on the ground/concrete, cable ramps for personal/vehicle traffic.
* occasionally a 6" PVC under a lawn or driveway

590.4(H) says protect from damage, doesn't prohibit on-the-dirt.
590.4(B)(2)
Exception: Single insulated conductors shall be permitted where installed for the purpose(s) specified in 590.3(C), where accessible only to qualified persons.

BTW, MI is an "insulated conductor" and it doesn't not need to be enclosed in any covering.

All that aside, there aren't excuses for things like abrasion protection, but running a short distance on the ground wouldn't be one of my concerns if the type allows it.
 
Don's post just popped up- fully agree; that's why type is important- does 310 (R**) or 400 (W or SC) apply.

If the NEC doesn't prohibit something, it's generally allowed; only sometimes is a practice specifically allowed.

I've been referring to single conductors. I've done a lot of temporary setups using single conductors (always W or SC); they're almost never run in conduit*- on the ground/concrete, cable ramps for personal/vehicle traffic.
* occasionally a 6" PVC under a lawn or driveway

590.4(H) says protect from damage, doesn't prohibit on-the-dirt.
590.4(B)(2)


BTW, MI is an "insulated conductor" and it doesn't not need to be enclosed in any covering.

All that aside, there aren't excuses for things like abrasion protection, but running a short distance on the ground wouldn't be one of my concerns if the type allows it.
Thank you, I appreciate the code citation, I had overlooked the exception. I wish there was a more clear definition of free air in the NEC.
 
Since it is a dual rated cable and the only rating that is permitted is the RHH rating and that makes the parent text in 310.10 apply. That requires the conductors to be installed in a Chapter 3 wiring method.

As far as the free air ampacity, even if it was permitted, you have an issue with the terminal ampacity rating rules in 110.14(C). The ampacity of the termination is limited to those found inTable 310.16, unless specifically marked for use with the ampacities from other tables.

As far as Article 590. 590.2(A) says that unless modified in 590, all of the other code rules apply. There is nothing that permits a single conductor of a type shown in 310.4 to be installed without being in a Chapter 3 wiring method.
This is a permanent installation which is only occasionally used, and I agree that the terminals are within enclosures and not in free air and I know they are only rated for 75c (and not rated for fine braid conductors). I am stepping into a new world here and finding the lack of workmanship is astonishing. Thank you.
 
can you show me where it is allowed, even for a temporary installation? 590.4 (H).I know abrasion protection is required, and I know that the conductors need a listed mechanical lug or crimp connector, but I can not find where insulated conductors can be installed without a covering anywhere in the nec.

DLO is a legitimate cable type often used in the past as portable cord and in DC motor wiring. It is fine strand with each individual conductor tinned for corrosion with a 2 kV insulation that is oil resistant. Jacket is very low durometer so highly flexible. It is a NEMA specification so UL won’t test. It is typically CSA Listed so legal as far as an NRTL is concerned but not a recognized type in the cord list in NEC so must be used in non-NEC applications.
 
AFAICT, DLO is not an NEC recognized flexible cord type nor a Chapter 3 wiring method. Yes, there is DLO that's also marked at RHH/RHW-2, but to the NEC, it's RHH/RHW-2. (I much rather people use type W if they need fine-strand/flexible and are under 600 volts.)

I have lots of experience in non-NEC environments (mining, marine) where we aren’t encumbered by ULs NIMBY policies.

DLO will be almost always dual rated RHW-2 or RW90 even though it vastly exceeds both ratings. Type R is a catch-all for generally any cable with a rubberized jacket. The jacket is CPE which is the same material used in mining trailing cables where it gets drug across the ground, rocks, etc., all day long. It was originally developed to connect a locomotive generator to the motor which is a high vibration and oily nasty environment hence the name. It’s also designed for maximum flexibility which is an advantage with tight radiates on many poorly designed DC systems from a bending radius point of view. It is this flexibility and toughness that makes it vastly preferred over W.

Type W eschews the tinning. It uses EPDM as the insulation/jacket which is significantly less flexible and less abrasion resistant with about the same thickness. It is considered light duty in the mining business. The flat version is used as submersible pump cable. A lot of it doesn’t bend much at all and is a pain to work with. It gets stiffer over time.

The ultimate jacket for toughness is TPU. It is stiffer than either of these and a royal pain to terminate it but if you are worried about tearing it up, this is it. It is an option for the hard rock miners and I’ve seen it occasionally in SO type cords but it is horrible to work with for the most part. So you will see it sold as some other cable type but with the TPU jacket.

That’s from a purely engineering point of view. But there is a major hassle with DLO. NEC has never recognized it as a type of flexible cord even though it obviously is. Even in its original use it’s intended as permanent wiring inside a wire way , not a “super cord” beyond SO ratings. Most of it is rated “for CT use” but not exposed run rated. Type RW90 and RHW-2 are designations for permanent wiring. So this is very annoying but you have to run it in some kind of wire way. A cable tray is fine but it has to be continuous. At the ends of the tray it needs a piece of flex or something to run inside unless you design the tray for continuous support and protection. That’s not the way I’d say 95% of the installations are actually done but that’s what Code calls for. Obvious running across the ground is sort of like having an infinitely wide tray with a solid bottom so that would be the correct derating factor. It’s not free air.

Even if you switch to W, portable cord rules still say no running through doorways, over rough edges, etc. as an example a particular generator installation I know of had 87 relaying but it was a very big loop. The 87 CTs were installed at the generator bushings (12,470) at one end and at the substation breaker 2500 feet away on the other side of the step up transformer, much like a power plant GSU. The 87 relays were set to trip if current differential exceeded 600 A! It kept tripping and they spent millions sending the generator (over 50 MW) off site to test on a test stand. Transformer and all wiring received obscenely expensive tests. Nothing found. All but swapped out all 87 relays and these were old monster induction disk relays that require someone in good shape just to remove them. Turns out the CT wiring didn’t have any grounding or plastic bushings. Over a period of about 30-40 years of vibration from the generator it finally cut through the jackets and intermittently grounded the CT. The permanent fix was to determinate, pull a little excess cable, slip on and screw in a plastic bushing, and land wiring again. Maybe a 15 minute job. I can’t remember how many times I’ve seen DLO and others destroyed costing tons of downtime because of poor installation practices.
 
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