SC feeder cable directly to circuit breaker (Square D)

[Neil Sakaitis]

I have #2 SC tails to CAMS. WIthout getting into the details of the setup and location, I was wondering if it is ok to directly feed the SC cable into a panel circuit breaker (Square D). My understanding is that only THHN wire should be used inside the panel, and lugs close more firmly around THHN wire. My understanding is that tightening down on an SC cable for Neutral and Ground on a buss lug could be acceptable, so long as you don't crush the SC cable much and the lug and cable are properly sized (no big space gap).

My concern has more to do with the physical connection between a panel circuit breaker and the SC cable. If there is no physical tension on the SC cable (held firmly at the panel), technically the screw down connection on a breaker will hold the SC cable in place.

In other words, a lug in a breaker panel should be similar to a lug on a disconnect panel, and care is taken not to crush the SC cable. But on a panel circuit breaker, my understanding is that the physical connection is not similar to a lug, and usually the requirement is only to use THHN cable with breakers.

Comments and thoughts ??

 

[RonHebbard]

I have #2 SC tails to CAMS. WIthout getting into the details of the setup and location, I was wondering if it is ok to directly feed the SC cable into a panel circuit breaker (Square D). My understanding is that only THHN wire should be used inside the panel, and lugs close more firmly around THHN wire. My understanding is that tightening down on an SC cable for Neutral and Ground on a buss lug could be acceptable, so long as you don't crush the SC cable much and the lug and cable are properly sized (no big space gap).

My concern has more to do with the physical connection between a panel circuit breaker and the SC cable. If there is no physical tension on the SC cable (held firmly at the panel), technically the screw down connection on a breaker will hold the SC cable in place.

In other words, a lug in a breaker panel should be similar to a lug on a disconnect panel, and care is taken not to crush the SC cable. But on a panel circuit breaker, my understanding is that the physical connection is not similar to a lug, and usually the requirement is only to use THHN cable with breakers.

Comments and thoughts ??

Personally, I'm not overly concerned about it, especially when you point out you're securing the cable physically at its entrance / exit point. The only thing you wrote that caught me seriously off guard was back near the top where you wrote "to directly feed the SC cable into a panel circuit breaker" leading me to think you're using the tails to supply power to the breaker rather than acquire power from the breaker. Many / most panel mounted breakers derive their source power directly from a breaker panel's buss bars but there are also breakers with lugs both in and out. If you're really concerned with crushing the strands within SC, you could over wrap the tiny strands with very thin gauge copper as is often used when terminating 400 Amp cams.
If you are really using your tails to supply power to the breaker, inspectors in my area are accepting of back-feeding breakers to supply a utility panel when the panel is not provided with a main breaker by its manufacturer.
Toodleoo!
Ron Hebbard.

 

[JD]

I believe it was Lex Products that was marketing tails where the strands at the tie-in point were fused. I am assuming that the breaker is the source of the power, and this is a temporary tie-in for a show being done by a qualified electrician.
Retired now, but most of the gigs I did over the last 20 years were cams to company switch. Prior to the mid 90's, often had to tie in tails. The critical point is that the lug on the circuit breaker is usually not designed to work with fine wire. The work-around we used to use (back in the 80's) was to crimp sleeves over the bare ends of the feeder, essentially making the last 1/2 inch a solid conductor. The danger of using SC on a breaker designed for thhn is that the strands migrate away from the pressure point resulting in a reduction of available gauge which could create a hot spot.

 

[BillConnerFASTC]

Not recommending you just slip it under the main feed lugs like I use to - hot - but on I'm trying to understand your concern on differences of SC and THHN stranded. I would think size (and of course material) is primary concern.

 

[Neil Sakaitis]

Sorry for not being clear on my post for source of power, I had no idea other direction was even an option, tails feeding individual breaker (not main). My post was referring to powering tails off of a 100A individual Square D panel breaker.

My concern was more about the breaker screw clamping down onto SC cable and possibly being less secure compared to THHN.

Someone mentioned about using the same thin copper foil wrapped around the SC cable similar to what is used in CAMS but I think someone else said that should not be done on a breaker, but perhaps they were referring to code, even though it is physically possible.

Basically just need to know can I secure SC safely into a panel breaker, and yes the panel breaker is equal to the main breaker on the distro, protecting the feeder.

Thanks guys !!!

 

[Neil Sakaitis]

JD also touched on some of my concerns, that a panel breaker is not designed (although will work) for soft stranded copper (like SC), as well as the possibility of the screw creating a hot spot as the cable crushes under it, essentially reducing the capacity of the cable.

To be honest, I am tempted to use the same copper foil wrap used on CAMS, but I know the code guys here might not agree using that on a panel breaker connection, even though it would distribute physical load on the screw connection better.

 

[STEVETERRY]

I have #2 SC tails to CAMS. WIthout getting into the details of the setup and location, I was wondering if it is ok to directly feed the SC cable into a panel circuit breaker (Square D). My understanding is that only THHN wire should be used inside the panel, and lugs close more firmly around THHN wire. My understanding is that tightening down on an SC cable for Neutral and Ground on a buss lug could be acceptable, so long as you don't crush the SC cable much and the lug and cable are properly sized (no big space gap).

My concern has more to do with the physical connection between a panel circuit breaker and the SC cable. If there is no physical tension on the SC cable (held firmly at the panel), technically the screw down connection on a breaker will hold the SC cable in place.

In other words, a lug in a breaker panel should be similar to a lug on a disconnect panel, and care is taken not to crush the SC cable. But on a panel circuit breaker, my understanding is that the physical connection is not similar to a lug, and usually the requirement is only to use THHN cable with breakers.

Comments and thoughts ??

The lugs on that general purpose breaker are not listed for connection of portable feeder cable with# #30AWG Class K stranding such as the type SC you mention.

However, lugs listed for Class K are a relatively recent invention, and would not be likely to appear on general purpose breakers--they are typically on only the latest types of Company Switch.

The history is that road crews have been connecting Class K feeder to this type of breaker for many years. Their solution? Cut back the feeder at each stop to get rid of the knarled-up #30AWG strands.

Another solution? Add a wrap of copper foil--the kind you get with cam-type feeder connector. It works wonders for feeder longevity.

Or, if you are a really code-compliant type of stagehand--carry a set of adapters to THHN, using class K lugs to mate with your SC feeder.

ST

 

[STEVETERRY]

Not recommending you just slip it under the main feed lugs like I use to - hot - but on I'm trying to understand your concern on differences of SC and THHN stranded. I would think size (and of course material) is primary concern.

It's about stranding-

THHN=19 or 37 strands for 4/0 AWG
Class K portable feeders (such as type SC): 2029 strands of #30AWG for 4/0 AWG conductors

#30AWG does not do well on normal set-screw lugs where the screw bears directly on the conductor.
Also, for a given AWG, a class K conductor has a larger outer diameter than the same AWG THHN conductor. It might not even fit into the lug without cutting strands.

ST

 

[RonHebbard]

I believe it was Lex Products that was marketing tails where the strands at the tie-in point were fused. I am assuming that the breaker is the source of the power, and this is a temporary tie-in for a show being done by a qualified electrician.
Retired now, but most of the gigs I did over the last 20 years were cams to company switch. Prior to the mid 90's, often had to tie in tails. The critical point is that the lug on the circuit breaker is usually not designed to work with fine wire. The work-around we used to use (back in the 80's) was to crimp sleeves over the bare ends of the feeder, essentially making the last 1/2 inch a solid conductor. The danger of using SC on a breaker designed for thhn is that the strands migrate away from the pressure point resulting in a reduction of available gauge which could create a hot spot.

Would you please elaborate on your / Lex's term "fused"? I'm especially interested to learn how this is different from tinning which I always believed created hardening which didn't conform well in lugs leading to smaller areas of contact thus hot spots / poor contact / conduction / heating / burning and other nasty happenings. Yes. Please elaborate as to Lex's version of fusing of the extra fine strands and how this is different / beneficial compared to soldering / lightly tinning.
Toodleoo!
Ron Hebbard.

 

[Chris15]

Would you please elaborate on your / Lex's term "fused"? I'm especially interested to learn how this is different from tinning which I always believed created hardening which didn't conform well in lugs leading to smaller areas of contact thus hot spots / poor contact / conduction / heating / burning and other nasty happenings. Yes. Please elaborate as to Lex's version of fusing of the extra fine strands and how this is different / beneficial compared to soldering / lightly tinning.
Toodleoo!
Ron Hebbard.

My understanding is that not tinning mains was around the conductor warming during use and that having a tendency to soften solder to the point of melting. From there comes both distortion leading to loss of secure contact, and the potential for worse things associated with liquid metal in a mains connection, does this still hold?

 

[JD]

Would you please elaborate on your / Lex's term "fused"? I'm especially interested to learn how this is different from tinning which I always believed created hardening which didn't conform well in lugs leading to smaller areas of contact thus hot spots / poor contact / conduction / heating / burning and other nasty happenings. Yes. Please elaborate as to Lex's version of fusing of the extra fine strands and how this is different / beneficial compared to soldering / lightly tinning.
Toodleoo!
Ron Hebbard.

I was just at their site and don't see them listed anymore. Only saw one set about 5 years back, definitely NOT tinned. Don't know what the process was but the strands were almost welded together. You could still see the grain of the strands, in the end, but even where slightly deformed by use in lugs, it almost acted like solid copper. Somewhat disappointed that what's up there now is just a cut bare end, but I suspect people didn't like them for some reason, or it was too easy for a house electrician to snip them off by accident.

At one time, they were pictured as such on the site and there had been a notation about the termination, but I don't recall what they called it.

 

[Neil Sakaitis]

In all honesty, the "screws" on a 100A or 125A breaker are more like lugs from a clamping perspective, I just installed the SC cable and it clamped well, even without the copper foil. The neutral and ground were obviously not an issue as they were clamped into dedicated lugs (properly sized) that screwed right onto the breaker panel neutral and ground buss bars. In all honesty, I am surprised that there is not more people on here that have had to tap directly onto breakers. I can't imagine Company Switches conveniently waiting for touring crews to show up in churches, schools, auditoriums, ice rinks, gymnasiums, etc. I would think a lot of patching would be done like this for smaller shows or venues (SC cable directly into breakers).

Either way, as someone mentioned here, once the wire is tight (not necessarily torqued), and the wire is secure and not pulling, should be fine.

Thanks for your feedback !!

 

[ship]

I note ferrules are not mentioned above. All correct in expansion and contraction of fine strand conductors "setteling" a bit after loading, than in the next use the contact not being in tension once the conductors settle - seen lots of from 30A thru 60A and above problems in this same concept, in the 60A plug, yearly inspections. Just fixed a Smart Pack with melt down in similar reasons of overall cause. I normally ask any 30 to 60A plug I install comes back to see me after the first use, but it never happens.

After initial loading, one should verify proper torque, than all should be fine for now - but yearly inspections is not a bad thing as with temporary install fittings welded or otherwise.

 

[MikeJ]

I note ferrules are not mentioned above. All correct in expansion and contraction of fine strand conductors "setteling" a bit after loading, than in the next use the contact not being in tension once the conductors settle - seen lots of from 30A thru 60A and above problems in this same concept, in the 60A plug, yearly inspections. Just fixed a Smart Pack with melt down in similar reasons of overall cause. I normally ask any 30 to 60A plug I install comes back to see me after the first use, but it never happens.

After initial loading, one should verify proper torque, than all should be fine for now - but yearly inspections is not a bad thing as with temporary install fittings welded or otherwise.

True, I find that L21/30 is the most common I use that terminals will become loose over time and melt.

On the original subject of tying into standard Square D type of breakers, I do find this to be pretty common, in non-traditional venues. I even have spare 100a breakers to add to panels temporarily, as long as the panel has extra capacity. A freshly striped #2 will fit into a Square d breaker.

 

[Jay Ashworth]

I missed this up at the top of the thread, but someone said that you'll be physically strain-relieving the tails outside the box?

 

[MikeJ]

Definitely strain relief the tails. An actual clamp down connector where it exits the box is best, but sometimes(often) these do not exist. I have been in a few ballrooms, there there is nothing but a hole in the box. While its not ideal or code, ziptieing the tails to a screwhole, bolt or even through an extra ground lug, will be better than nothing. I Have even bought new lugs and strain reliefs, installed them in a venues box, and left them there, because I had no faith in the ability of the "house electricians" to fix anything, and were continuing to do very unsafe things.

 

[Jay Ashworth]

I might be wrong, but I don't think that's *enough* on something this size. I would assume you'd have to use those Chinese finger pulls I can't remember the name of, and a structurally-mounted hook, either one per cable, or bundle the cables and put one on all 4, no?

What size are we talking about for 100A? 0AWG?

 

[MikeJ]

#2 is typical for 100A.

 

[Jay Ashworth]

Ok, I was close. #2 is *just* big enough to be considering individual ones, I guess, right?

 

[MikeJ]

Some real disconnects have a clamp that is essentially a flat bar or channel that clamps down with each cable laid out flat in one row entering the enclosure, though I have seen a lot that have no clamp, just a 2-4" hole with a plastic ring to protect from the sharp edge, other times I will find large romex type clamps on the enclosure, especially in small ballrooms.

With #2, in a pinch some heavy duty zip ties will hold the whole bundle, but again not Idea. A small nylon climbing sling, or some 1" webbing makes a good strain relief for things like a feeder run hanging from a tall structure, they grip smaller cable better than a span set. Also its key to have tails long enough that the Cams can be sitting on the floor, and the weight of the connectors are not hanging on the tails.

As far as putting individual wires through their own clamps/holes, some people will bring up the risk of eddy currents being introduced from conductors running through closed holes in the chassis. I am not an electrical engineer so I cannot speak to the validity of this concern, though I must note that I have never seen an entertainment PD where each cam was not going through its own hole in the chassis, so I have to wonder why the same thing would pose a problem at the other end of the cable.