ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
dsk 13
Admin 8
doc 3
Recent Posts
Bathroom electrical
by doc. 08/19/17 06:53 AM
electircal ageing test on IPC
by SIAME. 08/15/17 02:43 AM
electrical aging test on IPC
by gfretwell. 08/15/17 12:27 AM
"Line level" audio on Cat 5?
by gfretwell. 08/08/17 10:39 PM
Fire alarm phone lines and color coding
by gfretwell. 08/08/17 10:26 PM
New in the Gallery:
Gallery Test
Popular Topics(Views)
240,033 Are you busy
175,645 Re: Forum
167,876 Need opinion
Who's Online Now
0 registered members (), 83 guests, and 12 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#211297 - 10/03/13 12:43 PM Can I use a 600W Toggle dimmer in a 20A circuit?  
Hormel1144  Offline
New Member
Joined: Oct 2013
Posts: 1
NYC
Hello: I'd like to install a GE toggle-style dimmer in a 20A circuit. My concern is that the maximum load the dimmer is rated for in a single gang setup is 600W (it is downrated for multiple gang setups). This works out to a load capacity of 5A or less, in a circuit where the overcurrent protection will happily pass 20A before tripping; or enough to fry the device at least 4 times over. I understand that the code allows fixture pigtails to be sized to the max wattage of the fixture, regardless of the ampacity of the supply, because the maximum load on the pigtail will never be more than the fixture's maximum wattage. The issue here, however, is that the dimmer feeds into 12ga house wiring, and it is possible that in the future multiple fixtures could be attached to the leg, drawing as much as 2400w! We would then have a circuit which was not fully sized to handle the load permitted by the overcurrent protection. Wouldn't this violate the code?


2017 / 2014 NEC & Related Books and Study Guides

#211309 - 10/03/13 10:38 PM Re: Can I use a 600W Toggle dimmer in a 20A circuit? [Re: Hormel1144]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,858
Brick, NJ USA
IMHO, your concern at the time of installation is that you do not exceed the rating of the device controling the load.

The circuit is protected by the 20 amp OCP, which is compliant.

For example; you install 6 recess fixtures with 75 watt lamps, totaling 450 watts. The load on the device is within spec, even if it is two ganged.

Some time after you do the above; someone replaces the lamps with 150 watt lamps! The dimmer takes the bullet!!

Code compliance is 'at the time of installation/inspection'. There is no crystal ball, no lady reading the future, and the NEC is not 'idiot proof'.

A 120 volt 20 amp circuit calcs to 2400 watts, max load for non-continuous, and would be compliant. Common trade practice is NOT to load any circuit to 'max'.


John

#211313 - 10/04/13 01:30 AM Re: Can I use a 600W Toggle dimmer in a 20A circuit? [Re: Hormel1144]  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,103
Estero,Fl,usa
This is an interesting question. I suspect the real answer would be if U/L added the requirement of a fusible link in the device to blow if the allowable current was exceeded but, as far as I know it is not in the listing standard.
I suspect from experience that the triac would simply short and make it a switch.
Dimmers seem to fail "on".




Greg Fretwell

#211316 - 10/04/13 08:00 PM Re: Can I use a 600W Toggle dimmer in a 20A circuit? [Re: Hormel1144]  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
Ever try to find a dimmer rated for the full ampacity of a circuit? Good luck - and, if you find one, it will have a metal cover the size of a dinner plate, just to dissipate the heat.

Even most light switches are not rated for the full current- look closely, and you'll find plenty with straps stamped "10A."

It appears there has never been a requirement for a switch to be capable of anything more than controlling the intended load.


#211320 - 10/04/13 09:38 PM Re: Can I use a 600W Toggle dimmer in a 20A circuit? [Re: Hormel1144]  
BigB  Offline
Member
Joined: Mar 2004
Posts: 719
Tucson, AZ USA
This brings up a topic which is a pet peeve with me, inspectors who will try to enforce "idiot proofing". There is nothing in the code that I know of that requires us to go over the minimum requirements "in case" someone comes later and adds something. The "what ifs" could go on forever and my answer to them is whoever does the "what if" at a later date will be responsible for whatever is needed at that time.



Member Spotlight
Tom
Tom
Shinnston, WV USA
Posts: 1,044
Joined: January 2001
Show All Member Profiles 
Featured:

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

 

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.012s Queries: 15 (0.003s) Memory: 0.7719 MB (Peak: 0.9139 MB) Zlib enabled. Server Time: 2017-08-21 15:46:45 UTC