8AWG THHN for 50A Service

[Judge]

So I just picked up my 2020 Magnitude SV34 over the weekend and downloaded all of the documentation from the Customer Resource Site. In the process of planning some mods and upgrades.

I am getting ready to put in a Progressive Industries HW50C Hardwired EMS after the Transfer Switch to protect the coach from any power issues with Shore Power or the Generator. As I was prepping for the install, I saw that Thor used 8AWG THHN wire running from the Transfer Switch to the WFCO so I went to Home Depot and picked up some 8AWG THHN to connect in the HW50C.

Then as I was looking at the Thor schematics for my rig, it says that 6AWG should have been run from the Transfer Switch to the WFCO as well as from the Generator and Shore Power points to the Transfer Switch.

Best I can tell from my research, 8AWG THHN should be good for up to 50A.

Should I be concerned at all that the Thor Schematic calls for 6AWG and manufacturing ran 8AWG?

Could be a misprint or the original design called for the 6AWG as a margin for safety.

The HW50C also calls for 6AWG after reading its manual. Since the coach seems to be wired with 8..... no sense going to 6 for a rather short run.

[javelin]

Seems no one wants to touch this one......but I did stumble on a link that seems to show (if I read it correctly), your 120vac single phase THHN #8 copper conductors rated for 55 amps.......but if you scroll down to the next table on that link where they rate voltage drops (limited to 3 %) vs conductor length, there is no 50 amp entry.

I am not sure if this link jives with appropriate/current Electrical Codes, but I would “expect” Thor would not risk an electrical code violation in their designs......famous last words. You should verify with Thor that the “typo” is exactly that and not a factory substitution. I thought maybe Cavie (retired electrician) might have some current code books he can refer to for this one. Nice coach by the way.


http://encorewire.com/wp-content/upl...%20voltage.pdf

[halfprice]

Time to call thor and progressive ind

[Judge]

Originally Posted by javelin

Seems no one wants to touch this one......but I did stumble on a link that seems to show (if I read it correctly), your 120vac single phase THHN #8 copper conductors rated for 55 amps.......but if you scroll down to the next table on that link where they rate voltage drops (limited to 3 %) vs conductor length, there is no 50 amp entry.

I am not sure if this link jives with appropriate/current Electrical Codes, but I would “expect” Thor would not risk an electrical code violation in their designs......famous last words. You should verify with Thor that the “typo” is exactly that and not a factory substitution. I thought maybe Cavie (retired electrician) might have some current code books he can refer to for this one. Nice coach by the way.


http://encorewire.com/wp-content/upl...%20voltage.pdf

Your information is inline with what I have been able to find. I am not overly concerned because all of the information says it is rated for 55A.

My best estimate is the longest run of the wire is from the generator to the Transfer Switch and that is between 15' - 20' at most. The run from the Shore Power connector is under 15'. From everything I've read anything under 25' is safe for 8/3 THHN at 50A and the voltage drop would be 2% or so based on how it is run.

I did e-mail Thor with their diagram and a picture of the wires to tell them what I found and see how they respond. I will report back what they have to say once I hear from them.

I did install the HW50C last night and it works like a champ.

[Bob Denman]

And here I am: opening up the thread only because I figured that "8AWG THHN" had to be a typo in the thread title...
But I'm glad to hear that you've got a handle on the project: the best of luck to you with your new RV!

[Beau388]

Originally Posted by Judge

So I just picked up my 2020 Magnitude SV34 over the weekend and downloaded all of the documentation from the Customer Resource Site. In the process of planning some mods and upgrades.

I am getting ready to put in a Progressive Industries HW50C Hardwired EMS after the Transfer Switch to protect the coach from any power issues with Shore Power or the Generator. As I was prepping for the install, I saw that Thor used 8AWG THHN wire running from the Transfer Switch to the WFCO so I went to Home Depot and picked up some 8AWG THHN to connect in the HW50C.

Then as I was looking at the Thor schematics for my rig, it says that 6AWG should have been run from the Transfer Switch to the WFCO as well as from the Generator and Shore Power points to the Transfer Switch.

Best I can tell from my research, 8AWG THHN should be good for up to 50A.

Should I be concerned at all that the Thor Schematic calls for 6AWG and manufacturing ran 8AWG?

Could be a misprint or the original design called for the 6AWG as a margin for safety.

The HW50C also calls for 6AWG after reading its manual. Since the coach seems to be wired with 8..... no sense going to 6 for a rather short run.

There are two reasons to specify a particular wire gauge wire: voltage drop for the run and heat of the wire when delivering max current. Most tables give the wire gauge for voltage drop for a specific solid wire length. Wire gauge tables are different for solid wire and TNNH. What worries me about using multi strand wire is way it is clamped. I firmly believe that a crimped ferrule should be used to terminate multi-strand wire before it is clamped into the device. This is the only way to ensure a good connection equal to a solid wire .That said id the device has a sliding U clamp instead of a simple screw clamp it is ok.

[Judge]

Originally Posted by Beau388

There are two reasons to specify a particular wire gauge wire: voltage drop for the run and heat of the wire when delivering max current. Most tables give the wire gauge for voltage drop for a specific solid wire length. Wire gauge tables are different for solid wire and TNNH. What worries me about using multi strand wire is way it is clamped. I firmly believe that a crimped ferrule should be used to terminate multi-strand wire before it is clamped into the device. This is the only way to ensure a good connection equal to a solid wire .That said id the device has a sliding U clamp instead of a simple screw clamp it is ok.

You make good points..... but unfortunately Thor doesn't always follow best practices... like not adding a sub-panel for the AC output of the Inverters they install.

I'm not an electrician or electrical expert but when wire reaches a certain gauge, doesn't it only come in stranded options?

In any case, the THHN wire Thor uses is put into the connection and screwed down. I followed the same approach when adding the EMS.... although I did use crimped connectors for the grounding wires in the EMS.

The good news is that the runs are relatively short and flexible conduit has been used.

[raffaelli]

There are different ratings for the wire depending on if it is run as a single conductor open air conductor or not. Due to heat dissipation, the rating is higher as single conductor or in a 3 conductor cable. How is it run in your rig?

[Judge]

Originally Posted by raffaelli

There are different ratings for the wire depending on if it is run as a single conductor open air conductor or not. Due to heat dissipation, the rating is higher as single conductor or in a 3 conductor cable. How is it run in your rig?

Thor ran 8/3 THHN in a flexible conduit from the Shore Power connection point to the Transfer Switch and another run from the Generator to the Transfer Switch. Then the same configuration from the Transfer Switch to the Power Distribution Panel.

Of the three runs, the longest is probably about 15 feet with the rest being shorter.

[Judge]

Been talking to Thor about the discrepancy between the schematics and the 50A wiring in my coach. It took them a couple days to respond because they wanted to talk to the engineers.

At first they said that the generator to the transfer switch was supposed to be 8AWG because it provided a lower load and from the Shore Power to the Transfer Switch and Transfer Switch to the Load Center was supposed to be 6AWG and they were going to revise the schematics.

Then I had to tell them that after closer inspection, the generator and the Shore Power to the Transfer Switch appear to actually be 6AWG but from the Transfer Switch to the Load Center were 8AWG wire.

I said that it would appear my coach was wired incorrectly based on what they were saying and the schematics showed.

They then told me to take as many pictures as possible and send them in so they could review them. They said they would determine if it is a recall situation.

As I took a picture of each wire going into the WFCO Load Center, the two hot wires and ground wire are 8AWG and the neutral wire is 6AWG. I documented this all in the pictures that I sent to Thor.

I also sent them pictures of the loose screws rolling around the transfer switch I found as well.

I suspect I will hear from them again tomorrow.

[Judge]

So after a week I finally have an official answer from Thor's electrical engineers. Here is what they told me:



The 8 gauge wire is OK, per the NEC Table310.15(B)(16); included sheet. The 8 GA wire is “THHN @ 90 deg” and has an ampacity of 55 Amps. The conduit has three current caring conductors (Black, Red, & White), so we do not need to de-rate the wire. The distance from the transfer switch to the load center is less than 10 ft.

The single wires are mainly used on units with long distances between the generator and the transfer switch, installed in liquid tight. The generator has internal 35A breakers. I’m not sure when we changed or why we are using the single wires to the load center.

The print does show “6-3 w/ground” from the generator to the transfer switch, the shore cord to the transfer switch and the transfer switch to the load center. We will be changing this drawing to reflect this information


I felt like the 8AWG should be sufficient... and safe... based on the length of the run and at least Thor is confirming that and changing their documentation. And I have an e-mail from them in case something would happen.

[Popfla]

Originally Posted by Judge

I felt like the 8AWG should be sufficient... and safe... based on the length of the run and at least Thor is confirming that and changing their documentation. And I have an e-mail from them in case something would happen.

Always best to have it in writing. I even do that with my contacts with Thor and CW - I email them rather than call them, and save the emails to a dedicated file. Always a good idea to CYA.

[Judge]

Agreed.....

I already had to repair a manufacturing and General RV snafu over the weekend.

During the PDI, we had a water leak inside the coach when running the kitchen sink. The service department said the flexible drain hose in the slide was a bit short and came out of the fitting going into the grey tank when the slide was moving in and out. The said they made some changes to the routing of the flexible drain hose and said it wouldn't happen again.

Well..... while sterilizing the fresh water tank, we had water leaking int the coach when running the kitchen sink this weekend. Shame on me for not checking it more closely after it was supposed to be repaired by General RV's service during the PDI.

Turns out Thor could have used a flexible drain hose that was at least a foot longer. I read a post a while back where I believe someone else had a similar issue with their slide and kitchen sink drain and they used a pool filter hose to solve that problem.

The service guy who tried to fix it during the PDI used a clamp to hold the hose in place and screwed it into the slide floor and a piece of wood that also had a a bunch of AC electrical connections screwed to it. Since the hose and drain connection into the grey tank is stationary, as soon as the slide moved the clamp screwed to the floor pulled the drain hose out of the grey tank fitting allowing the water to leak onto the floor..... and allowed water to leak all over the AC wiring there.

I was able to move the clamp they installed and mount it differently to help keep the hose secured to the grey tank fitting. I think this will be a temporary repair and I am going to find an appropriate flexible pool filter hose to add some length and mount it better than the factory did.

I'm sure this is just the first of many modifications to improve upon Thor's design and manufacturing.

[Radioman]

Originally Posted by Judge

So I just picked up my 2020 Magnitude SV34 over the weekend and downloaded all of the documentation from the Customer Resource Site. In the process of planning some mods and upgrades.

I am getting ready to put in a Progressive Industries HW50C Hardwired EMS after the Transfer Switch to protect the coach from any power issues with Shore Power or the Generator. As I was prepping for the install, I saw that Thor used 8AWG THHN wire running from the Transfer Switch to the WFCO so I went to Home Depot and picked up some 8AWG THHN to connect in the HW50C.

Then as I was looking at the Thor schematics for my rig, it says that 6AWG should have been run from the Transfer Switch to the WFCO as well as from the Generator and Shore Power points to the Transfer Switch.

Best I can tell from my research, 8AWG THHN should be good for up to 50A.

Should I be concerned at all that the Thor Schematic calls for 6AWG and manufacturing ran 8AWG?

Could be a misprint or the original design called for the 6AWG as a margin for safety.

The HW50C also calls for 6AWG after reading its manual. Since the coach seems to be wired with 8..... no sense going to 6 for a rather short run.

The 50 amp plug in cable is #6, 30 amp is #10. That’s what I would use in either requirement inside or out. My rig is 30 amp, if I’m plugged in over 30 feet I have an extension using #6. I check voltages at each end under load. I will oversized wire if the connectors will accept it and if it’s already handy.