ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Shout Box
Recent Posts
MRI LED lights dimmer control replacement - wow!
by Potseal. 01/19/18 08:52 PM
VDE 0100 to introduce AFCIs
by sparky. 01/19/18 08:03 PM
Video: Inventor of the GFCI self-testing shocks
by Bill Addiss. 01/17/18 11:11 PM
FPE in Germany
by HotLine1. 01/17/18 07:07 PM
Fujifilm Recalls Power Adapter Wall Plugs
by Admin. 01/16/18 07:04 PM
New in the Gallery:
Housebilding DIY wiring
SE cable question
Who's Online Now
0 registered members (), 16 guests, and 13 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 2 1 2
Conductor Ampacity #3018
08/02/01 03:40 PM
08/02/01 03:40 PM
F
Frank Cinker  Offline OP
Member
Joined: Jul 2001
Posts: 311
Pennsylvania
In general, a no. 14 awg. with thhn insulation can safely carry 25 amps according to table 310.16. Switch and receptacle terminals as well as circuit breaker terminals are typically rated 75 deg. C. max. which limits circuit current capability to 15 amps. My question is why don't manufacturers make 90 deg. C terminals so table 310.16 can be used to it's fullest? Is it purely for economical reasons?

Work Gear for Electricians and the Trades
Re: Conductor Ampacity #3019
08/02/01 03:56 PM
08/02/01 03:56 PM
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,890
NY, USA
Good question Frank,

I think that one problem would be that the higher terminal temperatures would be affecting the operation of thermal breakers.

Bill

Re: Conductor Ampacity #3020
08/02/01 04:14 PM
08/02/01 04:14 PM
R
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
And who is going to accept an electrical system where the parts are operating at 194 degrees F? Also this heat production costs money. It is wasted energy.
Don(resqcapt19)


Don(resqcapt19)
Re: Conductor Ampacity #3021
08/02/01 08:49 PM
08/02/01 08:49 PM
A
Anonymous
Unregistered

I agree with Don on all points.
It's nice that wires can carry that much juice. But heat is a warning sign that something is wrong. So for safety's sake, wires need to remain cool. No one wants to touch a 150° F wallplate. Such a temperature should be a clue that a hazard exists.

If we start running 25 A over 14 AWG, where is the safety margin when the OCPD allows 200% for a minute or two? 50 A on 14 AWG would turn a junction box into a toaster even with 200° C insulation.

The insulation doesn't keep the wire from getting hot. It just resists degradation and melting at that temperature.

The hotter (actual temperature) the wires are, the higher resistance is.

Re: Conductor Ampacity #3022
08/03/01 12:21 AM
08/03/01 12:21 AM
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,890
NY, USA
Frank,

Some breakers may be rated 60C which would need further derating (conductor ampacity) for them to operate properly and be in compliance.

Wasn't there some older ones at 40C too?

Bill

Re: Conductor Ampacity #3023
08/03/01 12:58 AM
08/03/01 12:58 AM
A
Anonymous
Unregistered

It seems like I still see 40°C a lot. Perhaps I need to pay more attention to that.

Re: Conductor Ampacity #3024
08/03/01 08:47 AM
08/03/01 08:47 AM
M
Matt M  Offline
Member
Joined: Mar 2001
Posts: 93
Laporte, MN, USA
Gentlemen,

Are we not technically bound by section 110-14c to using the 60 degree rating of the conductors for circuits rated 100 amps or less, or marked for #s 14 through #1 conductors, unless that we can prove that every last termination involved is rated for the higher temperature?

I was told that the large 40 C stamp that you see on the side of some breakers is not the actual rating of the termination. If you notice, most of these breakers also state that they are suitable for use with 60 C or 75 C rated conductors. It sure would be nice to get this clarified.

Matt

Re: Conductor Ampacity #3025
08/03/01 10:25 AM
08/03/01 10:25 AM
R
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
The 40°C marking on breakers is usually the maximum ambient temperature that the breaker is rated for.
110-14(c) only requies that the current on the circuit does not exceed the 60°C ampacity. We can use the 75° and 90°C ampacities for derating or adjustment purposes.
Don(resqcapt19)


Don(resqcapt19)
Re: Conductor Ampacity #3026
08/03/01 12:08 PM
08/03/01 12:08 PM
M
Matt M  Offline
Member
Joined: Mar 2001
Posts: 93
Laporte, MN, USA
Don,

I agree with everything you said. But just to clarify further, if every termination on the circuit as described in 210-14c is rated for 75 C or more, we can use the ampacity of the wires listed in the 75 C column, even if derating is not called for on a particular circuit. Do you agree?

Matt

Re: Conductor Ampacity #3027
08/03/01 12:35 PM
08/03/01 12:35 PM
F
Frank Cinker  Offline OP
Member
Joined: Jul 2001
Posts: 311
Pennsylvania
Don,

Take Matt's question one level higher. If every termination on the circuit as described in 210-14c is rated for 90 C or more, can we use the ampacity of the wires listed in the 90 deg. C column, even if derating is not called for on a particular circuit? If for no other reason, in theory only? That was the intent of my original posted question.
[Linked Image]

Page 1 of 2 1 2

Featured:

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman

 

Member Spotlight
HCE727
HCE727
Delaware County, PA, USA
Posts: 186
Joined: November 2005
Show All Member Profiles 
Top Posters(30 Days)
Admin 20
sparky 15
Potseal 15
Popular Topics(Views)
243,566 Are you busy
180,366 Re: Forum
170,844 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.6.1
(Release build 20180101)
Page Time: 0.021s Queries: 15 (0.004s) Memory: 1.0196 MB (Peak: 1.1967 MB) Zlib enabled. Server Time: 2018-01-20 21:04:36 UTC