Hmm... I wonder why it's ampacity is so different. I'll have to look it up in NFPA 79 at work.
23amps and 14gauge wire, only used in panel?
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Hmm... I wonder why it's ampacity is so different. I'll have to look it up in NFPA 79 at work.
I was looking at NEC chart 310.15 not the NFPA chart. So I might be wrong.
ingchr1
Well-Known Member
This UL guide should help in answering a lot of questions on cable types and their applications:
UL Wire and Cable Marking and Application Guide
I'm used to seeing type SIS and/or MTW wire in control circuits. Not saying that it's what should be used in a brew panel, just stating what I'm used to seeing in industrial/power plant applications.
UL Wire and Cable Marking and Application Guide
I'm used to seeing type SIS and/or MTW wire in control circuits. Not saying that it's what should be used in a brew panel, just stating what I'm used to seeing in industrial/power plant applications.
That is great info from the UL, but we are talking about the wire you use inside the control box. But thanks for providing that info.
NFPA 70 is the NEC - 310.15 is the right table.
I checked with NFPA 79 and it didn't help.
I think the only difference between mtw and thhn is rating at 75c vs 90c . (I found some MTW at work that was rated at 75c)
I guess that it never hurts to upsize the wire.
ingchr1
Well-Known Member
Just adding some info to the conversation on cable types and their ratings, outside of the NEC and NFPA.
Now if I were wiring controls for an enclosed control panel for my home brew, then I would use the most readily available stranded 12 gauge wire that I could find, rated to the proper voltage. Weather it be THHN, MTW, SIS, etc.
NFPA 70 is the NEC - 310.15 is the right table.
I checked with NFPA 79 and it didn't help.
I think the only difference between mtw and thhn is rating at 75c vs 90c . (I found some MTW at work that was rated at 75c)
Says 105C in the link I posted. As stated, the rating of the terminations determines the column used in the ampacity chart. EDIT: Except of course for derating.
ingchr1
Well-Known Member
This is correct, the terminations are going to determine the overall temperature/ampacity rating. I think NEC article 110 talks about this (my NEC is at work, don't have a copy at home).
ingchr1
Well-Known Member
NFPA 70 is the NEC - 310.15 is the right table.
I checked with NFPA 79 and it didn't help.
I think the only difference between mtw and thhn is rating at 75c vs 90c . (I found some MTW at work that was rated at 75c)
The UL link I posted lists MTW at 90C for dry, but I guess that's probably the minimum per the current standard (if the wire is UL rated).
ingchr1
Well-Known Member
Wires carrying element power I would use #10.
augiedoggy
Well-Known Member
Some of the xerox machinery I service uses heating elements and relays and the used #14 wire inside the electric area going to the main relays and triac.... over the years some of these wires have become discolored at the ends and hardened from heat... this heat and damage could only be from the 17-18 amp load on those wires.. Although its more of an issue in the connectors in the heating element wires as Ive seen them crumble and melt over the years and had to replace many.
I guess they saved a good amount on $$ over the thousands of machines they manufactured by going with 14 gauge instead of 12 or 10. but like I was reminded before why take the shortcut here on one panel? sure it will work but heavier wire would be the better choice.
Yeah... just saying but the overcurrent protection for #14 thhn/thwn is 15amps, #12 is 20amps and #10 is 30amps... I don't care what kind of philosophical spin you put on it. If the terminals are rated for 75 degrees (which most all are) then you use the 75 degree column.
augiedoggy
Well-Known Member
I think the point of this thread is they are saying those values dont apply for this kind of environment?
augiedoggy
Well-Known Member
I'm not the one saying this.
I have no knowledge of this either as I go by the standards you mentioned above... Haven't you read the thread? I believe this is the main point of the discussion here..
I did read the thread and that is why I confirmed the wire sizes and overcurrent protection required for the wires. There is no exception for control panels in the code and I think this thread is very misleading.
I was reading it right off the spool - so I guess it depends.
Yep! This is just a friendly conversation about wire types and some sharing and learning of the NEC. I did look at NFPA 79 last night and it agreed with Jerz - 14awg = 15a, 12awg = 20a, 10awg = 30a, etc, without specifying any difference between THHN, MTW, or others that I dont recall off hand.
But - NFPA 79 is more about wiring practices within machine tool electrical panels. It assumes initial ampacities from NFPA 70 - NEC.
You go by the temperature rating of your teminals... that's all fine and dandy that the spool spells out 90degrees and so does thhn/thwn for that manner BUT you go by the temperature rating of the terminals which will be 75 degrees so that is the column you go by. Ultimately you can do whatever you want though.
augiedoggy
Well-Known Member
And I was just offering my experiences with machinery I service and the long term effects of the current on the wiring in some cases...
BTW I took a look at some of the wiring harnesses in my garage and most of the wiring for the heating elements is 12 gauge not 10 as I originally thought (which makes more sense). and the heat damage on those was mainly at the spade connectors so I believe poor connections cause things to heat up and it had nothing to do with the choice of wiring as I originally thought it could have.
It is completely legal and safe to use #12 SO cord for hooking up 25amp elements per NEC table 400.5(A) (Allowable Ampacities of flexible cords) as long as there are only two conductors are current carrying.
ingchr1
Well-Known Member
Even if using type SO, I personally would still upsize to #10 to allow some additional margin.
I agree... but it is a good point that #12/3 SO cord could be used for the 5500W heating elements at 240V I guess. I've got #10/3 STOW cord with 30amp cord and plugs... It would save a little money plus the #12 is easier to work with than the #10... so very interesting point in this particular application. My concern might be the fuse prematurely blowing with about 23 amps worth of load on it but...
ingchr1
Well-Known Member
For peace of mind for added margin to the cables rating, I'd gladly spend a few extra bucks. Really, what are we talking here maybe 50 cents more per foot at most?
Closer to a buck a foot - but whatever makes you comfortable. (Home Depot for instance is $0.80/ft more)
I'm absolutely certain that there is plenty of safety margin built into the ampacity tables already.
It's not worth arguing for me - it's black and white and in a code book.
ingchr1
Well-Known Member
Who's arguing? I never said #12 SO was unacceptable, all I said was if it was my system I would build additional margin into it by using #10. And for me the extra minimal cost is not going to hurt my wallet.
EDIT: Code wise I do not think #12 SO (rated at 25A) is acceptable for a 23A load. The codes are going to require the wire to be rated 125% of the rated load. So in this case one would need a 30A rated cable.
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