110 v system: any link between neutral and earth?

[niekbeem]

My girlfriend and I have put a deposit on a very nice 1990 Airstream 345LE motorhome recently and are planning to shipping it and importing it into The Netherlands soon.

Over here we use 220v, so in order to have all the 110v systems in the motorhome function properly when on 220v shore-power, I must purchase a proper step-down transformer.
I found a serious transformer with 3kW power, but it operates on a so called “Center Tapped Earth”.

This transformer is a heavy duty on-site transformer, ip44, and they designed this Center Tapped Earth so that , when the transformer gets physically damaged, an operator can only be “electrified” by 55v instead of 110v , which is a safety feature.

As a side effect this also means that parts in the 110v electrical system of the MoHo that have somehow their neutral connected to the earth, receive 55v instead of 110v , if my theory is correct. And that’s not what we want of course, because the transformer thinks that there is a shortcut and will shut down.

This is what the tech guy from the manufacturer says:

If you use our isolation transformer CM3300/010/PT for your vehicle, it could work without problem. We are aware of users operating USA sourced equipment from yellow portable tool transformers without issues.
However, if there is a connection in your vehicle between neutral and earth somewhere, this would clash with the ‘centre-tap earth’ output from our transformer. Then there would be an electrical short across half of the transformer output. The transformer should trip out very quickly before damage is caused. Your campervan would see 55V only until the protection trips out.

So, my question:
Does anyone know if there are parts in the original 110v electrical system of the MoHo that have somehow their neutral connected to the earth?

Or: if anyone has a good advice on a serious , external, weatherproof, step-down transformer, I would really love to hear some advice.

Thanks!
Niek/ Amsterdam.

[azflycaster]

The standard here is to keep the neutral and ground (earth) separate. They are tied together at the power pedestal at the campground.

[niekbeem]

Thanks!
So, theoretically this transformer will work properly?

Could you think of a reason why one would tie neutral and earth together in a motorhome?

Thanks again!
Niek/ Amsterdam.

[martin300662]

I highly recommend these Niek

They simply plug into a regular 220v supply and outlet can be wired to a Nema standard plug (https://airlinktransformers.com/prod...er-uk-us3010hw).

I have mine in a Peli case and leave it under the motorhome when camping.

I also have the same transformer that comes configured in an enclosure with standard US outlets. It is wired into my workshop so always have a 2 x 15amp 120v supply (https://airlinktransformers.com/prod...rter-uk-us3002)

[martin300662]

I forgot to add the site transformers aren't designed for constant load and so will burn out if you use them to give a constant 120v supply....

I had one, it died after a few weeks.

[niekbeem]

That’s a great advice !
I didn’t know that the site transformers aren’t designed for a constant load.

I also found this transformer, but (like yours) , if I’d buy it, I should find a place to install it. Your Peli-case sounds like a proper solution, I’ll think about it!

Thanks.
Niek/ Amsterdam.

[niekbeem]

PS:

Did you mount your incoming and outgoing power-connectors on the outside of the Peli Case?

[richard5933]

Even if the design is for neutral and ground to be separated in the motor home, you will want to verify as much as possible before connecting, especially in a vintage rig where it's impossible to know what previous owners have done.

For example, on our 1974 coach there was a 120v roof vent. It should have been wired with a single hot conductor and a single neutral. Somewhere along the way the neutral must have failed, as someone connected the neutral side of the fan to the chassis. This gave the fan a hot and a ground. It worked, but the first time we plugged in to a GFCI pedestal the GFCI tripped. It saw current on the ground that shouldn't have been there.

Not to difficult to check each circuit and major appliance to confirm.

[niekbeem]

Yeah, that’s exactly what I mean: we don’t know (yet) what the previous owners installed and how.

So it’s starting to turn out that these site transformers might not be a good idea to use as a motorhome step-down transformer.

Thanks.

[martin300662]

Yes, I have a 240v/16amp waterproof inlet the connect to the the campsite/home power and a RV 120v/30amp outlet to allow me to use my standard Furion 30amp cord set.

There is noting stopping you running the cables via grommets/fly lead and then the cables are permanently attached. Just makes them more cumbersome to handle.

Do keep in mind some of the bigger motorhome have 120v/50amp shore power connectors (4 cable) you will only be able to supply 120v/30amp using these transformers.

[richard5933]

There are not that many 120v appliances in a vintage rig... Have you considered just converting the whole rig to 240v?

[martin300662]

Originally Posted by richard5933

There are not that many 120v appliances in a vintage rig... Have you considered just converting the whole rig to 240v?

Biggest issue is the AC. Typically 240v roof top AC cost over double the 110v equivalent.

And of course the fridge.....

[richard5933]

Originally Posted by martin300662

Biggest issue is the AC. Typically 240v roof top AC cost over double the 110v equivalent.

And of course the fridge.....

The fridge is pretty low current compared to the a/c unit, and if it's still a propane fridge should be limited to the heating element for use when plugged in.

The a/c unit is probably going to be the difficult one either way - expensive to replace and likely difficult to run from a transformer due to the high current draw of the compressor.

[martin300662]

Originally Posted by richard5933

The a/c unit is probably going to be the difficult one either way - expensive to replace and likely difficult to run from a transformer due to the high current draw of the compressor.

.....and totally unnecessary in Europe (where we don't even have AC at home). Far easier to ditch the AC and fit a couple of roof vents, one blowing in one sucking out which creates a nice breeze through the motorhome.

[Air345Fly]

Are the 120v appliances in the AS able to run at 50 Hz? Running
60 Hz motors and transformers at 50 Hz is hard on them unless
they are designed to handle 50 Hz.

A properly designed transformer should not burn out unless
overloaded. I notice that the transformer that you mentioned,
CM3300/010/P, is only rated at 750VA continuous duty. That is
the spec that you should consider. The intermittent duty is
only useful to cover the surges when you start something like the AC.

The same company does offer the CM5000/210/PT. That has
2.5 KVA continuous duty, which comes closer to providing the
full power you might need.

[Boom Sounds]

The other advantage of the Airlink transformer over the yellow box version is that it has soft start. Theoretically, this limits initial current draw thereby stopping you switching off your (and possibly your Neighbour's) powe when plugged in and taking initial draw. I think Airlink (or EU equivalent) is the way to go, they are tried and tested on American Motorhomes.

The other alternative is to get rid of all the 110v gear and switch to 220v. You would need to consider viability, cost and also whether the genny can output 220v. I think (although not sure) that some of the Onan gennys could be set to output 220v.

[Air345Fly]

Originally Posted by Boom Sounds

You would need to consider viability, cost and also whether the genny can output 220v. I think (although not sure) that some of the Onan gennys could be set to output 220v.

The original Onan generator cannot be converted to 240 volts.
It is also a 60 Hz unit.

[niekbeem]

I think, since most of the European campsites only provide 6amp or 10amp (rarely 16amp) a 3Kw transformer will do in my (upcoming) 345LE.

Though, I'm starting to understand that, although built very strong, these on-site transformers aren't the thing that I should choose for, because of this Center Tapped Earth.

A better option would be Airlink or Xenteq.

Also: converting my rig into 220v is gonna be a real hassle. Not for me.

Thanks for all the advice.
Niek/ Amsterdam

[bkahler]

As mentioned previously the coach wiring keeps the neutral and ground separate. However, if your 345 has a generator you need to keep in mind that when the generator transfer relay kicks in (i.e. power coming from the generator) the transfer relay makes a connection between neutral and ground.

This may not be a problem with how you plan on using the transformer but it is something to keep in mind.

Brad

[niekbeem]

It sounds more and more that a Center Tapped Earth-transformer is not wise to utilise as a 220v > 110v step-down-transformer for motorhomes.

Thanks again for all advice.
Niek/ Amsterdam.