# COMMUNITY FORUM

doit4me2

05:34AM | 02/17/05
Member Since: 02/16/05
I need to run a buried sheathed electrical cable to my motor home and wire in a 30 amp circuit to my main distribution panel. what size wire should I use for a distance of 140 Ft??

Tom O

02:18PM | 02/17/05
Member Since: 09/17/02
Two more items are needed to give you a fairly accurate answer.

What voltage is this circuit?

How many amps are you actually going to be using? The calculation can be done for the entire 30 amps, but it will return a larger wire size.

Tom

doit4me2

06:27AM | 02/20/05
Member Since: 02/16/05
Thanks for answering. It is 120vac, and rated for 30 amps per the Motor Home manufacture, But actual use will be charging batts and lights. So 20 amps work load should suffice. I was thinking about 10/2 w Ground. Let me know if this adequate.

Tom O

01:17PM | 02/21/05
Member Since: 09/17/02
My calculator shows a voltage drop of 6.5 volts (5.4%) using the numbers you posted. This is just a wee bit on the high side, but as long as you don't try to start & run any motor loads, you should be OK with #10.

Tom

sakk50

12:13PM | 02/25/05
Member Since: 02/24/05
If you are going to run this wire "buried" or underground, use 10-2 U.F. (Underground Feeder) cable instead of regular sheathed electrical cable.

MistressEll

10:57AM | 02/27/05
Member Since: 01/30/05
the 2005 Edition of the 2002 NEC addresses this very issue. Oh, by the way take special note that the rules for connections for mobile homes have been expanded. Also note that Addition of Appendix H to the NEC:

Several Sections within Article 240, including 240.100(A) and (C), specifically require that conductor temperature ratings not be exceeded under short-circuit conditons. In the past, users of the Code had to access IEEE, IEC, or the Canadian Electrical Code to determine THESE TEMPERATURES. The addition of Annex H therefore imporves the usability of the NEC.

These fomula are typically used whenever the ampere rating of the overcurrent device is several sizes larger than the ampacity of the conductor. In these cases it is much easier to cause CONDUCTOR DAMAGE due to EXCESS HEAT under short-circuit conditions.

I'm assuming you are intending to run this off of a branch connector from your home power, yes?

Also note that the Table 344.24 was relocated to Chapter 9, Table 2, to CLARIFY that the requirements apply to conduit types OTHER THAN RMC as well! You are NOT allowed to under wire your required 30 amp circuit, esp with 10/2 sheathed electrical cable with a seperate ground in EMT underground out to mobile home. You need to do more reading, you've received "pat" answers that are not correct, old un-amended 2002 NEC nor current 2005 edition of 2002 NEC as amended!

MistressEll

11:06AM | 02/27/05
Member Since: 01/30/05
A 30 amp fuse or circuit breaker is NOT designed to react to conductor overloads where the conductor is under-rated to the breaker and/or length, and your distance is too far for 10 awg.

Where are you that you are allowed to bury sheathed electrical cable 2-wire for a 30 amp circuit outdoors? with common "house ground"?!? You're outdoors, where's your GFCI?

By the way, you have to go by the Motor Home MFG. just like you have to use the maximum wattage rating on a lighting fixture. You'll end up overloading your conductors from house to mobile home and wearing them out causing trouble. Got to use the proper distance, and proper rating for the conductors and for underground exteriors got to follow all of the codes, much stricter as you are going to a NON-dwelling situation.

Tom O

12:34PM | 02/27/05
Member Since: 09/17/02
My 2005 NEC must be missing a few pages. There are no appendix H, there isn't even an Annex H. Also, 240.100 applies for voltages greater than 600 volts.

I've also noticed in my code book that a motor home is not a mobile home, it is a recreational vehicle, and has its own article (551)

I admit that I assumed the original poster meant UF cable when he referred to buried sheathed electrical cable.

I am still looking for the requirement for ground fault protection as it regards 30 amp 120 volt circuit for this type of installation at a dwelling, or other type of property.

Also, Table 2 in Chapter 9 deals with bending radius of conduit or tubing, how does this apply to the posters question?

I feel that a 10-2 UF cable, connected to a 30 amp breaker at the source and a 30 amp 125 receptacle at the motor home without GFI protection is in compliance with the NEC, 2002 or 2005.

I thought maybe April 1st had come early :-)

doit4me2

02:41AM | 02/28/05
Member Since: 02/16/05
Thanks for everybody's input to this question

I was planning on running direct buried sheathed electrical cable inside of 1-1/2 conduit just to be safer. the circuit will be run from my main 200 amp panel (hince 175 ft). I will be using a GFCI Breaker at the main panel. This os for a motor home, not a mobile home and will be strictly to keep venting fans and batts charged up.

Wireman

08:59AM | 03/05/05
Member Since: 12/19/04
4me, there is no such thing as direct buried sheathed electrical cable. You must be talking about UF cable. Run the UF cable at the proper depth, protecting it at both ends with Schedule 80 pvc pipe and forget the 11/2" conduit. If you do run the conduit why would you bother trying to install UF cable in it instead of using standard wire such as thhn wire? If you use pvc conduit and number 10 wires you drop the conduit to a 1/2" size which will accommodate standard use boxes and the final result will look nice instead of having to install adapter after adapter to terminate in a nice outdoor receptacle box.

ron

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