Protecting the TRC/Southwire 40350 Transfer Switch

[LWBAZ]

In this thread…

www.irv2.com/forums/f278/transfer-switch-southwire-40350rvc-in-19-cornerstone-395924.html

… there was considerable discussion regarding the TRC/Southwire 40350 transfer switch Entegra is currently installing and the fact that its power protection features are, at least to some degree, “one and done.” In other words, the power protection features built into the 40350 transfer switch may indeed protect your coach from a major power issue, but if the problem is bad enough you will end up with a non-functioning transfer switch.

As such, the general consensus was that having a separate power protection device ahead of the 40350 transfer switch would be a good idea. Such devices are available from Progressive Industries – www.progressiveindustries.net – and Surge Guard (which is now owned by the same company that owns TRC) – rvpower.southwire.com/products/surge-protection. A number of owners participating in that thread indicated they have used such devices, portable or hard-wired, on current and/or previous motorhomes.

In my case, I’ve used a Progressive Industries EMS-PT50C portable unit on two previous motorhomes and have been very satisfied with it. The EMS-PT50C is the predecessor to the current P.I. EMS-PT50X. I kept the EMS-PT50C when we sold our Tiffin Allegro Bus since the new owner was already planning to purchase an EMS-PT50X.

Over the past several days, I was able to complete some modifications similar to what I'd done on the Allegro Bus. The photos below will illustrate, but the short version is that I cut the 50 amp cable that runs from the output side of the cord reel to the input side of the 40350 transfer switch, and installed a 50 amp female receptacle on the cord reel side of the cable and a 50 amp male plug on the transfer switch side of the cable.

After doing that, I determined the factory-installed cable I had cut wasn’t long enough to conveniently support what I wanted to do. The end coming out of the cord reel (on which I’d installed the female receptacle) was fine, but I needed/wanted a longer cable from the transfer switch. Fortunately, I had some 50 amp cable “in stock” in our onsite RV garage, so I cut a length of that about 7 feet long, wired the 50 amp plug on one end, and connected the other end to the input terminals on the 40350 transfer switch. At that point I was in business!

As you can see in the annotated photos below, with this setup I can, if necessary or desired:

1) Bypass the cord reel and my Progressive Industries EMS-PT50C such that shore power flows directly from a shore power pedestal to the 40350 transfer switch.

2) Bypass the cord reel while leaving the EMS-PT50C inline ahead of the 40350 transfer switch.

3) Bypass the EMS-PT50C while leaving the cord reel inline ahead of the 40350 transfer switch.

4) Have the cord reel and the EMS-PT50C both inline ahead of the 40350 transfer switch.

As you might expect, the normal setup will be #4 – with power flowing from the shore power pedestal to the cord reel to the EMS-PT50C to the 40350 transfer switch. In the event of a cord reel failure (relatively rare, but usually caused by failure of the rotating contacts buried deep inside the reel), I can quickly & easily bypass the reel. In the event of a major power issue, the EMS-PT50C will take the hit rather than the 40350 transfer switch, and if the EMS-PT50C ends up dead I can quickly and easily bypass it until a replacement arrives. And the good news is that all of these options are “plug & play” with no rewiring necessary or required.

To be clear, I’m not suggesting or recommending that anyone do what I did. I’m just documenting this approach for any owners who may be interested in doing something similar. Any questions or confusion, feel free to ask.

[Matt D]

Nice job Larry, as usual a very clean install and great documentation.

-Matt

[redbaron73]

I am considering doing the same thing with my install, but using a hardwire unit.

I am trying to decide if it would be better to use a wall mount receptacle for the output side of the shore reel and surge protector ILO plug ends for that side.

The advantage would be a bit cleaner look, and possibly better at cord organizing.

The disadvantage would be that I will have another set of lugs to check periodically.

For the plug ends, I am buying premade plugs (Conntek 14300 RV Power Cord 4-Foot RV 50 Amp Male Plug To Bare Wire https://www.amazon.com/dp/B001TO4YH6..._Y0jOBbVP7JZMP)

I can buy the same style for the receptical end, and wire as the OP did, but I wouldnt lessen the amount of lugs.

My only concern with adding recepticals and plugs is the potential for power loss/heat build up. Is there a standard or known information that would suggest that this is either ok, or a bad idea? By adding hardwire, you lose convenience but cut the amount of connections in half.

I know the OP used a different product, but it does demonstrate my desired install.

[oneknight]

Originally Posted by redbaron73

My only concern with adding recepticals and plugs is the potential for power loss/heat build up.

That is a real concern, and it is or should be a real concern to everyone who has a "plugin" style surge protector.
Every connection in the line adds resistance, which adds heat.
This effect gets worse over time. A setup that works fine when installed could cause a serious voltage drop 5 years later.

[W0GEN]

Originally Posted by oneknight

That is a real concern, and it is or should be a real concern to everyone who has a "plugin" style surge protector.
Every connection in the line adds resistance, which adds heat.
This effect gets worse over time. A setup that works fine when installed could cause a serious voltage drop 5 years later.

I use and would suggest using a anti oxidation compound on your high amp plugs. This will greatly reduce any future oxidation causing poor contact.

https://www.amazon.com/NO-OX-ID-Spec...70_&dpSrc=srch

[redbaron73]

Would it be safe to assume that hardwire is preferred over multiple plugs and recepticals? The inconvenience of dealing with a failure seems more desirable than the potential problem introduced by amp loss/heat gain.

[brobox]

Originally Posted by oneknight

That is a real concern, and it is or should be a real concern to everyone who has a "plugin" style surge protector.
Every connection in the line adds resistance, which adds heat.
This effect gets worse over time. A setup that works fine when installed could cause a serious voltage drop 5 years later.

I am running into that right now with my current shore power plugs with line loss to the EMS. I am on my way to the MH now to change plugs to see if there's a change, or if it might be with the new EMS.

[oneknight]

Originally Posted by redbaron73

Would it be safe to assume that hardwire is preferred over multiple plugs and recepticals? The inconvenience of dealing with a failure seems more desirable than the potential problem introduced by amp loss/heat gain.

It depends on your goal, as well as the frequency of failures.

Some, such as the OP here, prefer a quick plug and play solution for any foreseeable failure.

Others may not see the potential of failure as worth protecting to that level.

[redbaron73]

Originally Posted by oneknight

It depends on your goal, as well as the frequency of failures.

Some, such as the OP here, prefer a quick plug and play solution for any foreseeable failure.

Others may not see the potential of failure as worth protecting to that level.

The work done once is appealing. If I have a failure, and I have plugs, it's a 5min fix at most. Otherwise it could be an hour.

My concern is that we are heavy users in Texas heat, running all 3 acs, washer, dryer, etc. I can use 80amps easily. This is a pretty big load for sustained usage, and weak points will be found.

Is there a rule as to how much heat/load loss per connection that should be calculated?

[Tony Wilson]

Complex question.This is AC, not DC. Therefore the procedure would be to measure the impedance (not resistance) in ohms in each contact and then calculate the power generated in loss and converted into heat to know the temperature the contact will reach at a given current (ampere). This is electrical engineering at work. My recomendation... you want to have the lowest possible impedance from the electrical post to your transfer switch to not have voltage drop and produce heat. So the least possible plugues and outlets will help.

[brobox]

Originally Posted by brobox

I am running into that right now with my current shore power plugs with line loss to the EMS. I am on my way to the MH now to change plugs to see if there's a change, or if it might be with the new EMS.

It was not the plugs but line draw from the MH. Turned everything off and had 122v after the plugs

[oneknight]

Originally Posted by brobox

It was not the plugs but line draw from the MH. Turned everything off and had 122v after the plugs

It's the plugs, the wire, and how they all behave under load.

Zero current = zero voltage drop, right?

If you have a tenth of an ohm resistance and draw 10 amps through it.... hmmm, now I gotta remember ohms law... E=I*R... So 10* .1 = 1 volt dropped.

Now let's draw 50 amps? 50* .1 = 5 volts.

Now make that tenth amp 2 tenths. 50* .2 = 10 volts. TEN Volts. Your 122 volts just became 112!

With 2 tenth of an ohm resistance through the sum of all the wire and any connections.

And you can't measure this. An ohmmeter puts maybe 9 volts DC across the connection, simply not the same conditions as full power under load.
You have to measure voltage and current under actual power and load, and calculate resistance from that.

Really the best thing is just to shoot it with an IR Temp gun. When there is current and resistance there will be heat.

[Gary.Jones]

Although I understand the logic of protecting against failure in various systems, I believe that the more plugs and connections that you have in an electrical circuit, the more chance that you have for failure and the greater chance that you have for heat under heavy current loads. When it comes to electricity, my philosophy is to "keep it simple" and avoid needless complication.

If there is a failure in my shore power cord, or if I forget to unplug it and rip the plug or the power reel out of the coach, I will run the generator if power is needed and replace the whole power cord reel and cord. Simple: 4 screws in the floor and 4 screws connecting to the EMS. But I believe that the chances of that occurring are exceedingly low, above zero, but exceedingly low. We all have different priorities. I don't carry spare tires although a flat is a clear possibility... I don't have a spare refrigerator although this one may go on the fritz. If the worst happens, I will deal with it at the time.

Gary

[LWBAZ]

Two points:

1) As stated in the last paragraph of my post initiating this thread:

“I’m not suggesting or recommending that anyone do what I did. I’m just documenting this approach for any owners who may be interested in doing something similar.”

2) I ran this same set up for the better part of eight years on a 2010 Tiffin Allegro Bus with no ills effect. That coach had three roof A/C units, a residential refrigerator, four TV’s, etc. We live in Arizona and travel extensively in the southwest throughout the year, including the summer months when temperatures are routinely north of 105 to 110 degrees F.

If the configuration was failure prone or dangerous I suspect it would have become apparent by now.