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I am a hvac tech, but my question is I have 2awg stranded and my plug is 6awg, will it matter much if I cut some strands to fit my plug? the plug is 60amp 250vac for a piece of kitchen equipment if the matters.

  • And although you write "plug", is this the plug on the end of the flying lead attached to the appliance - or is it the "socket" you're attaching to the permanently installed wiring in the walls of the building? – brhans Sep 15 '19 at 14:00
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    If the connected equipment doesn't require more tan 60 amps, it is not particularly dangerous, but it is poor workmanship. –  Sep 15 '19 at 14:09
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    Dan, I am guessing that because you are hvac and this is for a kitchen, then this is personal work as opposed to professional. Given it's a kitchen item (oven/stove?) at 60 A, I assume the distance doesn't justify 2awg. Is that what was used from the breaker panel?? In any case, I'd use a splicer/reducer and tie in 6awg to the 2awg without damaging either. Put those reducers into a small box. – jonk Sep 15 '19 at 15:16
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    You should NEVER reduce a wire diameter by removing strands. You have no way to guarantee that all the strands are connected end to end anyway. This is why you should use pressure ferrules on the ends of high capacity wires to ensure all strands are connected. – Jack Creasey Sep 15 '19 at 15:57
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    @manassehkatz Thank goodness there are some sensible folks out there that try to conform to the rules. Cutting strands is just plain stupid apart from being against the rules. – Jack Creasey Sep 15 '19 at 19:09

1 Answers1

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AWG 2 reduced by 50% or increased in resistance by 200% becomes AWG 5 so AWG 6 plugs can tolerate a reduction in strands of 50% easily.

The power dissipated per foot of AWG 6 @ 0.32 mOhm/ft at 60 A = 1.2W/ft for internal wires which would barely make the wire warm and the AWG2 even less W/ft.

The connector screw contact resistance will be greater than the few mm reduction length/diameter in strands or 5.4 uohms/inch increase in resistance/pair, so I do not see any issues here.

Use a crimp lug or ferrule for termination.

Tony Stewart EE75
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    I reiterate....you cannot guarantee that all the strands are connected end to end. It's as simple as that. The ONLY way to guarantee a multi strand cable is correctly terminated is soldered or compression ferule. If you cut off a strand on one end you don't care if it's connected at the other. But if the strands you have left are not connected (bonded) at the other end you are reducing your wire size much more than you thought. It's just common sense. – Jack Creasey Sep 15 '19 at 18:53
  • AWG2 is overkill for 60A service yet you claim strand reduction is unsafe . How do you compute this? – Tony Stewart EE75 Sep 15 '19 at 18:45
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    No it is NOT adequate. The OP claims to be an HVAC tech …...and should know the rules. It's not worth discussing further, but IMO you are completely wrong to provide any form of validation to reducing the number of strands in a cable in ANY application. – Jack Creasey Sep 15 '19 at 18:43
  • Agreed : a crimp lug or ferrule is the proper termination for stranded wires, but choice of 50% is adequate here – Tony Stewart EE75 Sep 15 '19 at 18:39
  • That is true for the strands you terminated on one end …..but the strands you cut off ….are they guaranteed to be bonded on the other end. Screw terminals DO NOT clamp all the conductors and are only valid for single strand cable. Where you have multi-strand cable you should always use a compression ferule. The NEC demands you use the correct termination: https://www.ecmweb.com/code-basics/article-110-requirements-electrical-installations – Jack Creasey Sep 15 '19 at 18:18
  • Adequate torque on the wire bond to terminal screw is all that is needed (which any HVAC tech would know) for a gas-tight non oxidizing contact of 0.1mOhm for this size which at 60A is only 0.36W. Inadequate torque can lead to oxidation. Your assumptions are dubiousness and unqualified. – Tony Stewart EE75 Sep 15 '19 at 18:03
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    The individual strands in a bunch are only lightly connected at best….they may or may not be connected together due to the surface oxidation of the copper strands. If you have multicore cables you should either solder the ends or use a compression ferrule to ensure all the wires are bonded together. That fact that you so casually say this would be ok, shows you have no experience with high current circuits. What makes you think the individual strands are connected together? – Jack Creasey Sep 15 '19 at 18:00
  • Why Do you think strands are decoupled? They are not until they are separated. The assumption here is they are not separated for a significant gap and 50% would be better than AWG6 required FWIW @JackCreasey You do not have to choose which strands, just keep the bundle tight. – Tony Stewart EE75 Sep 15 '19 at 17:53
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    Very bad answer. You have no idea which strands work if you cannot guarantee ALL strands on the other end are bonded together. You should NEVER EVER reduce the strands on power cables. – Jack Creasey Sep 15 '19 at 17:52
  • I already agreed a compression sleeve either lug or ferrule. Why do yo persist? How would you quantify it/ – Tony Stewart EE75 Sep 15 '19 at 18:57
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    Because you still cannot guarantee that the wires you have left (after cutting some strands off) are actually bonded at the other end. You need to modify your answer. – Jack Creasey Sep 15 '19 at 19:03
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    This answer was migrated to diy.se, where engineering matters defer to the Electrical Code. As such, ***here***, it's a very, very, very bad answer. The electrical code says "iksnay, there are cheap and practical ways to do that thing if you need to". And that is that. If a factory wire chokedown were designed by an EE and run through the UL approval process, different deal. – Harper - Reinstate Monica Sep 15 '19 at 19:13
  • @JackCreasey what evidence do you have to support your supposition that a stranded cable has uncoupled strands? Meaning the resistance of 1 strand is not less than theoretical due to coupling or other strands in the cable length? Each strand is not insulated and the 50% of AWG2 is also adequate for 60A service. Regardless of coupling in the AWG2 cable? – Tony Stewart EE75 Sep 15 '19 at 19:16
  • @Harper can you define the design differences of a factory wire choke down by reference or imperical measurements? We’re not talking about cutting down a AWG6 cable – Tony Stewart EE75 Sep 15 '19 at 19:26
  • I can define the losses. Can you be more explicit? – Tony Stewart EE75 Sep 15 '19 at 19:28
  • @sunnyskyguy Ee75 it is a violation of the national electric code. A splice to a smaller size wire is the code compliant method for reducing wire size. As this is a duplicate the op also said it is 3 phase. Adding another layer of code that would prohibit just cutting. – Ed Beal Sep 17 '19 at 14:17
  • @EdBeal your assumption would be valid if the circuit demanded AWG2 but it only requires AWG6 for 60A , so it is still overkill unless a very long line then the strands are irrelevant as per my calculations – Tony Stewart EE75 Sep 17 '19 at 14:18
  • No code dose not allow for the modification of a conductor. The ONLY legal way to downsize is to pigtail / splice to a smaller size. Your calculations mean nothing to the code and that is the governing authority. I install oversized conductors all the time for voltage drop mitigation and if I could it would be way easier and cheaper to clip a few strands but this would not be legal. – Ed Beal Sep 17 '19 at 14:26
  • I see even if Physics says that is illogical given the circuit use. – Tony Stewart EE75 Sep 17 '19 at 14:28
  • Let’s say the HVAC load is a compressor that surges 500% of a normal load on startup then 50uOhm /cm / %strands might inject <2W for a fraction of seconds and does nothing on degrading short cct protection . The NEC and HVAC standards are not perfect for sizing wire on compressors for surge drop voltage but are safe for heat rise in cable components (AWG5 for 60A @ 75’C max) . IMHO my calculations are safe. But I dont have to pass inspection, just pass Laws of Physics and with low loss on startup and low temp rise. – Tony Stewart EE75 Sep 17 '19 at 14:57
  • I can only image the NEC made this rule to avoid poor mechanical strain relief installations. But there is no electrical rationale., that I can justify for it. Can you? @EdBeal – Tony Stewart EE75 Sep 17 '19 at 15:03
  • Yes, The rated ampacity of the wire is compromised, if it could be done not everyone would do it the same. Any difference in 3 phase can cause problems when paralleling 3 phase the same length , size wire and bonding method is required can you splice yes but be ready to have an inspector climb up your butt, er check everything with a fine tooth comb (even to the point of 4 point probe measurements to verify they were the same). The last point I would make it violates the UL listing of the wire and that alone is enough for a red flag. If the cord is two large for the clamp again red flag. – Ed Beal Sep 17 '19 at 18:01
  • But the compromise **is not electrical (or physics)** for this breaker rating or HVAC rating **was my point** and violations must have some mechanical reasons which were not presented here. Respect for rules must have some sanity check and respect for inspector’s job. I have deviated from UL rules in the past and got UL approval with Voltage drop proof. – Tony Stewart EE75 Sep 17 '19 at 18:06
  • That was for 10k production and alternate earth bonding method relying on welded stud thread resistance rather than a designated ,masked unpainted area on chassis to pass a 100 mOhm cordset earth R Spec with my << 100uOhm connection. – Tony Stewart EE75 Sep 17 '19 at 18:13
  • Jack et al, the strands are joined along the cable , so a short length of a few mm won’t matter much if a couple out of 20 or so strands won’t matter . Compute the loss in pwr!! @JackCreasey – Tony Stewart EE75 Jan 29 '21 at 22:53
  • @EdBeal What is the true loss of ampacity if 10% reduction of strands at one end only for 1cm ? – Tony Stewart EE75 Jan 29 '21 at 22:54
  • Tony, you can count strands and figure that one out on your own. I would not even suggest this as I would not sign for it as a code violation. Changing wire size to a smaller size with a listed device then smaller wire sure if it was for voltage drop but that is not what you suggest. I know inspectors that will flag connections with 1 or 2 strands not in the lug. If the components are properly sized the wire will fit! It may be tight and a real bugger I hate putting 500kcmil wire in 350-500 connectors at a 90 it is a PITA but it can be done. – Ed Beal Jan 30 '21 at 01:20
  • Ok I know it would be flagged, but from my physics point of view the thermal stress would be negligible because the disconnected strands would be electrically and thermally conducting in a very short distance., just as. my welded stud ground over paint was electrically better than compressed ring lug to an unpainted surface. My Physics and verified by UL – Tony Stewart EE75 Jan 30 '21 at 03:25