Electrical Management Systems questions

Hi Planning,

It's not broken, so don't fix it!

Planning wrote:
I just yesterday was examining photos I took of all components and noticed that they have it wired after the tfer switch, so that coach input goes through tfer switch, and then the output (either shore power or onboard Onan 5.5) becomes the EMS input. (I should have deduced that by seeing gen output readings on the EMS control panel for 3 years...??)

My question is, should I have it rewired to first in line, or leave it as is?

Planning wrote:
My question is, should I have it rewired to first in line, or leave it as is?

I would leave it as is. TS is not that sensitive to over/under voltage etc. Worst case you can bypass the switch or carry a spare. You want the main panel protected from all input and you have it as wired.

Planning wrote:
Mexico and other electric pros,

Slightly off-topic question.

When I purchased the RV, I specified to the dealer that I wanted the (separately purchased) Progressive EMS-HW50C hard-wire system installed as first in-line for all coach input, after the power cord but before the automatic transfer switch.

I just yesterday was examining photos I took of all components and noticed that they have it wired after the tfer switch, so that coach input goes through tfer switch, and then the output (either shore power or onboard Onan 5.5) becomes the EMS input. (I should have deduced that by seeing gen output readings on the EMS control panel for 3 years...??)

My question is, should I have it rewired to first in line, or leave it as is?

As you can see from the preceding posts, there is disagreement. I believe you need to leave it as is. Others feel just the opposite. My suggestion is to read the rationale that each side has put forward, and make your own informed decision.

Don't leave it as is because *I* said that is safest, but don't redo it because someone else says that is safest.

(We may both get some knowledge if someone answers my question above about what harm can be done if the EMS is after the transfer switch. One that will be stated is that it needs to be before the transfer switch to "protect" the transfer switch. Now, you have to decide if you would rather risk the transfer switch being damaged from bad shore power, or risk everything else in your RV being damaged from bad generator power.)

I really hope some will answer for the other side. I would like to be convinced by their arguments, but in 13 years of RVing, I have not been yet.

Mexico and other electric pros,

Slightly off-topic question.

When I purchased the RV, I specified to the dealer that I wanted the (separately purchased) Progressive EMS-HW50C hard-wire system installed as first in-line for all coach input, after the power cord but before the automatic transfer switch.

I just yesterday was examining photos I took of all components and noticed that they have it wired after the tfer switch, so that coach input goes through tfer switch, and then the output (either shore power or onboard Onan 5.5) becomes the EMS input. (I should have deduced that by seeing gen output readings on the EMS control panel for 3 years...??)

My question is, should I have it rewired to first in line, or leave it as is?

pianotuna wrote:
Hi Bobbo,

I can see a use for EMS with 50 amp. With 30 amp--not so much.

I have superior surge compared to what is available and use an Autoformer (boost and buck) to take care of low voltage.

I do have a way to limit my demand to 80% of what is available, so on 15 I limit to 12, 30 to 24, and 50 to 30.

An EMS to me would simply be another potential failure point.

I always check voltage under load and polarity before plugging into an unknown source.

Differing opinions are what make life interesting. You follow your muse and I will follow mine.

Ed_Gee wrote:
If one is paranoid about the extremely unlikely chance a generator could somehow fail in a damaging way, have at it and wire your EMS to include it, as outline in the many responses above.

Thank you. I think I will. And while I am at it, I will allow my paranoia to force me to carry fire extinguishers too.

(BTW, rather than call it paranoia, I prefer to call it being cautious. Maybe overly so, but I have never had a severe problem if I was being overly cautious.)

This is an open question to all who think the generator power should not go through the EMS. I have heard many times that it was not necessary. My question is, what harm can it do? If it is even potentially helpful and can't be harmful, then why not? If it can be harmful, how?

time2roll is correct although that generator is now ancient history.

The 12-turn Onan (6.5NH) was pure volts per hertz regulated. Self-regulated. Saturated field.

One burp and the next amplitude could take it to 150 volts.

It was a sturdy monster like the old Delco 20Kw railroad reefer generators powered by Detroit 2 or 3 cylinder 71 engines.

I loved these old Onans. 12-wire reconfigurable 120/240 stators. 1,200 RPM. Wish I could find one.

Ed_Gee wrote:
In my 40 years of RVing, I have NEVER heard of a generator failing in a way that could harm the electronics in an RV.

OK and I have read posts of a failed Onan or other brand regulator creating 140-160 volts output.
I would not have concern with an inverter-generator as it would shut down power if voltage was out of range.
The bypass does not turn off the actual surge protection but again that would be near impossible with any generator.

cavie wrote:

One slight correction. It is diagnosing the situation exactly correct. Open ground. In a main service panel the ground and neutral are bonded together. Every panel after that is a sub-panel and the neutral and grounds are kept separate.

The generator is the Power Company and is the place that the neutral and grounds are bonded. Since the generator is not bonded, the ground is not connected. Think OPEN. Hence the OPEN GROUND indicator. Someday Gen manufacturers are gonna wake up.

I disagree with this, and will just state why and move on. Both NEC and OSHA regs are pretty clear that the generator's frame replaces a grounding electrode, and the equipment grounding terminals of the generator's receptacles are to be connected to the generator frame. Unless there's an actual break in the equipment grounding conductor (ground wire), the EMS (or 3-light tester) is most certainly connected to the generator frame, yet diagnoses "open ground". Without an independent connection to the actual ground, the tester has no way of making a positive diagnosis.

As far as the manufacturers waking up goes, there are plenty of arguments that the floating output lowers the risk of shock in the event of a failure, the obvious example being if the outside case of powered equipment were to become "hot" while the user is in contact with an earth ground. There are opposite arguments, too. It's not a slam-dunk, clear issue for either approach.

Planning wrote:

dryfly wrote:


Planning......judging by your pictures you are successfully running an EMS with the modified male plug at the generator. Do you routinely do this or use the bypass feature of your EMS??

I invariably use the plug.

The only time I use the bypass feature is if I inadvertently forget to bring the plug, which has only happened once.

I do not use the generator often; the primary use is for needing power at the storage location for lights and battery charging while performing preventative maintenance duties.

It works well and seamlessly.

OK, then making and using the plug, or dongle shown above, sounds great and should do the trick.

I was under the impression that an accessory PI bypass kit was necessary if you want to go the bypass route, but just looked and it's a standard feature on the unit with remote readout model EMS-HW50C.

I think I got a plan now!

dryfly wrote:


Planning......judging by your pictures you are successfully running an EMS with the modified male plug at the generator. Do you routinely do this or use the bypass feature of your EMS??

I invariably use the plug.

The only time I use the bypass feature is if I inadvertently forget to bring the plug, which has only happened once.

I do not use the generator often; the primary use is for needing power at the storage location for lights and battery charging while performing preventative maintenance duties.

It works well and seamlessly.