What type of wire from 50 amp inlet to breaker panel?

belfert · April 23, 2020, 06:49:24 PM

I am relocating my breaker panels and will need to run new wire from my 50 amp inlet to the breaker panel. What type of wire should I use? I am currently using marine cable, but it is not UL listed for RV use. It is also tough to make a good connection at the breaker. What do they use in a production motorhome? (Not that a production motorhome is a good example.)

My brother is wiring his new home and I think he might have a long enough piece of 6/4 AWG Romex left over, but I don't know if the solid ground wire would be an issue. The other three wires are stranded.

Brassman · April 23, 2020, 10:39:08 PM

I'd think 50 amp service entrance cable (SE) would be the one. Your brother's 6/4 would probably do just fine. Cable for 50 amp electric ranges is like a 6/2, and 8 for the neutral and ground wires. Fine stranded cables don't directly hook up to residential. Limited number of wire strands for that, 9 and 12, but I'd check the number of strands for 6 gauge wire.

richard5933 · April 24, 2020, 05:57:07 AM

I used 6/4 SOOW cable to connect my shore power inlet to transfer switch and the transfer switch to the breaker panel. It's flexible enough to be snaked through the wire chase and is plenty heavy to carry the current.

In places where it could potentially rub I wrapped with heater hose for extra protection.

https://www.amazon.com/gp/product/B071XJ6YG4/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

It's quite easy to use fine-strand wires with mechanical terminal clamps like those found in transfer switches and breaker panels. Just put a crimped ferrule on the wire first. I've got 6-ga wire running between the shore power receptacle and the transfer switch in my bus, and on all connections to the screw-down terminals I used the ferrules. Makes for a very secure connection. Commonly used all throughout Europe.

Here's the crimping tool:

https://www.amazon.com/gp/product/B01CCC36SQ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

And here are the crimped ferrule:

https://www.amazon.com/gp/product/B01I7XB848/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Some will suggest tinning the ends of the fine-strand wires before connecting, but that has been shown to cause a weak connection over time. Using a ferrule creates a parallel surface for the terminal to clamp onto, and it will not weaken over time like solder will.

belfert · April 24, 2020, 01:29:21 PM

Quote from: richard5933 on April 24, 2020, 05:57:07 AM
I used 6/4 SOOW cable to connect my shore power inlet to transfer switch and the transfer switch to the breaker panel. It's flexible enough to be snaked through the wire chase and is plenty heavy to carry the current.

SOOW is just as bad as using marine cable in my mind. The reason for not wanting to use marine cable is no UL listing for use in an RV. SOOW cable can be purchased as UL listed, but it is not to be run through walls. The reality is that proper installation of marine wire is probably safer than Romex and such that is approved for RV use.

My thoughts are going towards using 6/3 MC (flexible metal conduit). My concern is how do I terminate the metal jacket properly at the Marinco inlet?

richard5933 · April 24, 2020, 03:40:41 PM

Quote from: belfert on April 24, 2020, 01:29:21 PM
SOOW is just as bad as using marine cable in my mind. The reason for not wanting to use marine cable is no UL listing for use in an RV. SOOW cable can be purchased as UL listed, but it is not to be run through walls. The reality is that proper installation of marine wire is probably safer than Romex and such that is approved for RV use.

My thoughts are going towards using 6/3 MC (flexible metal conduit). My concern is how do I terminate the metal jacket properly at the Marinco inlet?

Are Marinco inlets UL listed for use in an RV?

There is a version of 6/4 SOOW which is UL listed, but not sure if it specifically mentions for RV use.

https://www.wireandcableyourway.com/6-4-soow-portable-cord-600v-ul-csa.html

The biggest problem I faced using residential wiring in this application was trying to snake it through the places it needed to be routed. The flexibility of the SOOW made this much easier.

I agree that Romex should be avoided, since the solid wire can break/crack over time if there is any movement.

Wire and Cable has lots of other options for 6/4 cable.

belfert · April 24, 2020, 04:21:04 PM

Quote from: richard5933 on April 24, 2020, 03:40:41 PM
Are Marinco inlets UL listed for use in an RV?

I never checked on UL listing, but Marinco makes a whole line of stuff specifically for RVs under their Parkpower line. Lots of production RVs now use inlets compatible with Marinco.

My concern with using SOOW is less about UL and more about not using it inside walls. SOOW is really for portable power cords.

dtcerrato · April 24, 2020, 04:54:19 PM

We use a Marinco 50amp twist lock design on our bus for pole power. Can't beat marine grade. Imo.

Brassman · April 24, 2020, 09:35:06 PM

Though I try to do everything by NEC standards, are buses even subject to the Code.

richard5933 · April 25, 2020, 06:42:02 AM

I've also used Marinco for all the shore power connections, and find them to be high quality.

I guess it would be helpful to know the specific reasoning behind the general prohibition of using SOOW cable inside walls before being able to say whether they apply in our applications. One thing I've seen that made sense was being able to properly protect the cable from abrasion or puncture damage. Another possibility would be heat build-up, but I have not found anything specific about that.

One interesting thing I found while searching is that there are limited applications where use of SOOW cable in raceways was permitted. Not sure about your bus, but on mine almost all the wiring runs in raceways with removable metal covers. Some are behind the florescent light fixtures, and others are right out in the open like the raceway connecting the different electrical panels in the driver's area. In my bus, the flexible SOOW runs from the inlet in the lower electrical panel, through a raceway to the upper electrical panel where it terminates at the transfer switch. From there it continues to the breaker panel in the same panel. The generator is connected to the transfer switch via SOOW as well, but that cable for the most part is in the open along the ceiling of the bays.

An alternative would be to use flexible plastic conduit, and then pull four 6-ga conductors through it. More difficult to use, but it would provide better protection for the conductors.

dtcerrato · April 25, 2020, 06:57:02 AM

IMO lots of NEC codes are hair splitting so to speak. Some of what's been happening to "bending" the rules/regulations & bureaucracy during this unprecedented pandemic relates to how I think of it...
We used soow cable for USE (underground service electric) to out buildings a few hundred feet from the house. Candid conversation with electrical building inspectors refer to soow cable as "direct burial on steroids".
The mention of no soow in enclosures is a technicality In lots of ways it's better but it's "spec" say no. Oh well IMO.

richard5933 · April 25, 2020, 07:40:58 AM

Quote from: dtcerrato on April 25, 2020, 06:57:02 AM
IMO lots of NEC codes are hair splitting so to speak...

I think that this sums things up for me.

The cable I replaced when I installed the SOOW between our shore power inlet and the transfer switch was also SOOW-type cable. It had been in the raceway since 1974 and held up well. The problem which caused me to replace it was that Custom Coach only used 8-ga conductors instead of 6-ga, which gave me reason enough for the switch. Probably would never have been a problem, but once I saw that it was only 8-ga (and since things were already opened up for another project) there was no reason not to upgrade since the expense was minimal.

dtcerrato · April 25, 2020, 10:35:08 AM

10-4 on the 8 gauge - only the ground is permissible in 8 gauge on a 50 amp service.

belfert · April 25, 2020, 02:38:18 PM

My brother has a leftover 25 foot section of 6/3 Romex he will give me so that is the route I am going to go. The conductors are stranded except the ground which is solid.

kyle4501 · April 26, 2020, 12:47:37 PM

Quote from: dtcerrato on April 25, 2020, 10:35:08 AM
10-4 on the 8 gauge - only the ground is permissible in 8 gauge on a 50 amp service.

50A for most RVs isn't used as 220V, but is used as 2 separate 110v circuts - As such, I would advise using the same gauge wire for the ground as for the hot & neutral. May not be required by 'code' , but if the ground wire is needed, I don't want it being the weak link. . . .

As for SOOW cord - the insulation is designed to be exposed, not encapsulated. Some may last fine in conduit, others not so much.
Same goes for welding cable, I've seen lots with the insulation cracked & falling off.

As for marine cable - It is the best.
I wouldn't hesitate to use the best.