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#19673 - 12/31/02 11:30 PM Amp readings/Warm wires  
ThinkGood  Offline
Member
Joined: Aug 2002
Posts: 1,081
Milwaukee, WI
Here's something I noticed today::

The clothes dryer (installed by the previous) is connected to a receptacle such as:

[Linked Image]

via 10/2 with ground.

According to the current NEC, this is a violation. However, it was installed in 1996. I believe that it was OK then.

The appliance is rated 120/240V, 60Hz, Motor 4 Amps, Heater and Accessories 23 Amps.

The cable itself feels warm when the unit is running, as well as the double 30A breakers (tandem). Total length of cable from the receptacle to the service panel is approximately 30-something feet.

I used a meter with a clamp and came up with the following readings while the dryer was running:

Black = 22A
White = 24A

The panel's ground connection showed 2A.

The service entrance cable showed 24A/28A and 5A on the neutral, with about 2A on the ground.

When I shut the main breaker, everything read zero.

Your thoughts/ideas, please?


Work Gear for Electricians and the Trades

#19674 - 12/31/02 11:50 PM Re: Amp readings/Warm wires  
caselec  Offline
Member
Joined: Apr 2002
Posts: 558
San Jose, CA
Was it wired with 10-2 SE cable or 10-2 NM cable? If it was NM cable then the cable should be replaced with a 10-3 cable. It has never been permissible to use the bare wire of type NM cable as the grounded conductor (neutral). If 10-2 SE cable was used you may be OK since the bare wire of 2 conductor SE cable can be used as a grounded conductor. Does this circuit originate from the service panel or a sub panel? If it is coming from a sub panel the bare wire should not be connected to the equipment ground buss in the sub panel.

Curt


Curt Swartz

#19675 - 01/01/03 12:37 AM Re: Amp readings/Warm wires  
ThinkGood  Offline
Member
Joined: Aug 2002
Posts: 1,081
Milwaukee, WI
Hi, and thanks for the quick reply.

It's NMB...

Difficult to read the wording on the jacket, but looks like AMMCOFLEX and definitely 10-2 WITH GROUND TYPE NMB 600V (UL).

This is connected to the main service panel. I have to check again where the bare ground wire goes--I believe it is going to the ground bus. Is a bare wire permitted to go to the neutral bus? (This is a newer service, less than 2 years old, 200A with a separate ground and neutral bus, though they are bonded together.)

By the way...
I meant to ask in my original post--isn't the 30A breaker a bit close for the rating on the dryer? Figuring 4A for the motor and 23A for the rest, that's 27A, with a 30A breaker. Or, am I totally off since it's a double tandem breaker?


[This message has been edited by ThinkGood (edited 12-31-2002).]


#19676 - 01/01/03 03:18 AM Re: Amp readings/Warm wires  
nesparky  Offline
Member
Joined: Jun 2001
Posts: 642
omaha,ne
This is very common for that type of dryer plug 10-2G was used by a lot of low ballers in resi work. 10-3G is used now with the 1996 change that made that plug an existing only replacement. All the combined neutral and ground carries is the controls current. That is the 2 amps in your measurements.
A 2 pole 30 amp breaker has worked on dryers for years and is correct ( .8 x 30 = 24) just what you measured.
The place may have been built before the 1996 code was in effect in the area.
All in all unless something else is wrong with this circuit or it's wiring I would leave it alone.


ed

#19677 - 01/01/03 03:47 AM Re: Amp readings/Warm wires  
ThinkGood  Offline
Member
Joined: Aug 2002
Posts: 1,081
Milwaukee, WI
Thanks to both of you for your responses --
"low ball" sounds about right, especially by the looks of the way the 10-2 was installed. Quite a sloppy job.

What had concerned me the most was the warm cable and breakers. (Not hot, but warm enough to notice it.)

Just to clarify, as the receptacle is now wired with 10-3, are the [i]plugs[i] wired with 4 conductors somehow--that is, would the chassis of the dryer be grounded, and if so, how?


#19678 - 01/01/03 04:00 AM Re: Amp readings/Warm wires  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
The "warm" feeling is normal. You have to remember that when you load a conductor to the maximum permitted by Table 310.16, that the conductor will reach a temperature close that that shown in the table. For #10 with a 30 amp load and a 86°F ambient the conductor will reach a temperature of about 140°F. Your load is less than 30 amp and I expect the ambient temperature would be less than 86, but I would expect the conductor to feel warm, maybe 110 to 120°F.
Don


Don(resqcapt19)

#19679 - 01/01/03 04:56 AM Re: Amp readings/Warm wires  
lwinter31  Offline
Member
Joined: Nov 2002
Posts: 40
Texas
Thinkgood

The new rec's wired with 10/3wg have 4 contacts and use a "4wire" pigtail to the units. Most dryers and ranges come with a bonding strap from the chasis to the nuetral, you remove the strap on a "4wire" install and connect the equip. ground to the chasis and the nuetral to the normal nuetral lug. You should be able to do the same with older models. Hope this helps.

Larry


#19680 - 01/01/03 08:54 AM Re: Amp readings/Warm wires  
electure  Offline


Member
Joined: Dec 2000
Posts: 4,259
Fullerton, CA USA
I'd bet that the extra 2 amps on the white wire is the result of the motor running at less than its full load, rather than just the controls. (Mine's only got switches and a timer motor for controls).
Throw in a load of wet towels and the load's bound to go up...S


#19681 - 01/01/03 10:30 AM Re: Amp readings/Warm wires  
ThinkGood  Offline
Member
Joined: Aug 2002
Posts: 1,081
Milwaukee, WI
Thanks again, for the quick replies.

resqcapt19: Thanks. I don't have a copy of the NEC. (I'm trying to get into the trade, after being laid off from an internet-related job since May.)

lwinter31: Is this the receptacle to which you refer: [Linked Image]

electure: Interesting...this one has an "auto" setting and my wife did mention something once about wet towels, etc.

(One way to get out of laundry duty is to mess it up. Problem is, two can play that game--I won't have anything to wear so I don't even dare...) [Linked Image]

To all of you -- thanks again, and since this board has such a strong theme about codes and safety, I read that one of the largest causes of house fires is improper or clogged venting of clothes dryers!

[This message has been edited by ThinkGood (edited 01-01-2003).]



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