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#140687 04/20/04 08:24 AM
Joined: Apr 2004
Posts: 156
rad74ss Offline OP
I have a 380/3/50 to 220/1/50 transformer to supply the control circuit to an HVAC panel. Does the neutral conductor bond to earth ground like American 120V or go without like American 240V? These are all metal units with galvanized enclosures and false panels. With our 120V control we run a grounding conductor from the neutral terminal to the false panel and bond the panel to the enclosure, and the doors to the enclosure.

It seems like a simple and basic question, but I have been told that there is nothing simple or basic about Russian wiring.

Thank you.

Joined: Sep 2002
Posts: 1,498
C-H Offline
Welcome to ECN!

What is a false panel?

Someone told me the Russians do the grounding in their own way: Instead of bonding neutral and ground in the main panel, they bond in each equipment... I don't think it is true as it would introduce some problems.

The Russian system is indeed 220/380V and the neutral of the supply would be referenced to earth somewhere, most likely near the utility transformer. But I don't know what applies to a control transformer.

[This message has been edited by C-H (edited 04-20-2004).]

Joined: Apr 2004
Posts: 156
rad74ss Offline OP
I found a Russian electrical engineer who said they do bond the neutral to earth at the main panel. She hasn't worked there since the curtain fell though, and isn't sure how Russia is trying to adapt to modern codes. Apparently some of the wiring is still hanging around from the 40's, like my house!

A false panel is a seperate sheet metal panel we put all of our controls and starters on. We then mount it into the sheet metal enclosure, which contains weld in studs, with star washers,Keps nuts, and ground straps.

We run a wire from the neutral (L2)conductor of the transformer to a terminal and ground that terminal to the false panel with a green pigtail.

Does all 220(230) single phase in non-American countries have a neutral bonded to ground? I have read that New Zealand and Australia do. However I am still trying to get the M.E.N. system to stick in my brain.

Edit note: This transformer is integral to the HVAC unit. Incoming power is three phase wires to a main terminal block and a ground lug. There is no provision for neutral on the main power side.

[This message has been edited by rad74ss (edited 04-21-2004).]

Joined: Aug 2001
Posts: 7,520
Hi, and welcome to ECN.

I can't speak for Russia, but in Europe in general there are different neutral/grounding arrangements for utility supplies. Briefly:

(1) TN-C-S, the closest there is to the American system, with a neutral-ground bond at every service entrance and thus multiple grounds on the neutral where one xfmr supplies several premises. (Also known as PME -- Protective Multiple Earthing -- in the UK, and equivalent to the Australian MEN system.)

(2) TN-S. Neutral is grounded only at the xfmr, and a separate protective grounding conductor runs back to that point. No neutral-ground bonds are used at the service panel or anywhere else. Still found in the old parts of many British towns, but I don't think it's that common elsewhere.

(3) TT. Supply neutral is grounded, but the EGC/grounding system of the building is not bonded to the neutral at all. It is connected to a local ground rod only.

You might like to look at these diagrams in the reference area to see the arrangement of the different systems. They're drawn from a British perspective, but the basic principles apply to European as well.

When it comes to a control xfmr, you have what in NEC terms would be described as a separately derived system. Is this part of the HVAC panel itself, or a stand-alone unit which then uses building wiring to distribute the 220V power? That could affect any code requirements in different countries (e.g. the latter might come under the code whereas as integral xfmr would be part of the equipment rather than the building wiring and thus not covered).

Certainly if installing a xfmr as a stand-alone unit here to step-down from 415V to 220-240V it would be normal to bond one side of the secondary to ground.

[This message has been edited by pauluk (edited 04-20-2004).]

Joined: Dec 2001
Posts: 2,492
Another system that should probably be mentioned here is TN-C. Neutral is grounded at service entrance and at every receptacle, light fixture, etc. there's a jumper wire between ground and neutral. Has the advantage of only running 2 wires everywhere and was widely used in Germany until 1973 (Western)/1984 (GDR), mostly for upgrading existing installations. Neutral breaks will result in the appliance casing being at line potential, reversed polarity at some point will even cause the easily accessible ground terminals at the sockets to get hot. All extensions to such a system have to be wired with a separate ground wire freom the connection point to the old wiring.

TT systems require a GFI (RCD) to be fitted in almost all cases.

Generally 230V (or 200 in some countries) is a line-to-neutral voltage (also referred to as line-to ground potential), hence the neutral is supposed to be grounded.

Sorry if I'm showing my ignorance here, but what on earth does a 380V 3ph to 220V 1ph transformer do? Do you only have a 380V delta supply w/o neutral? Then it'd make perfect sense to me.

Joined: Dec 2001
Posts: 2,492
BTW, why are you that surrprised about the 40ies wiring? There are many US houses with knob&tube still in place!
I spent the last few years tearing out 1910s wiring out of my walls here in Austria, but some of the wiring (mostly ceiling lights) is still in service and holds up quite well.

OT, but recently I found a live 230V wire buried in plaster, no tape or anything, just cut! (Originally there were 3 wires feeding the light fixture, 2 seperatley switched phases for a big chandelier). At some point somebody installed a new junction box and thought he'd only need 1 phase, so he just ben one of the wires upwards and plastered over it. When it came to hooking up the fixture he didn't remember which phase was the dead one, and instead of checking he just twisted both together and hooked them up to the fixture. Ugh!

Joined: Jul 2004
Posts: 200
TN-C existed in UK too I believe... Apparently, according to the ol' codger I served time under, this was the purpose of the little gap in the plugtop case next to the earth pin; to run a 'fly' to some convenient earth [Linked Image]

As it happens, I recall as a youngster that my parents had an old fan heater with this fly springing out of the plugtop. Don't ever recall it being used tho' - just left coiled up.

Can't verify this's an awful long time ago!!

If hindsight were foresight, we'd all be millionaires!
Joined: Apr 2002
Posts: 2,527
Rad74—your post has been on the board for about 3 months and I apologize for overlooking it. There are a few things that are worth watching out for with this electrical equipment.

Fifty-hertz electromechanical equipment operated on typical 60Hz systems has varying success rates, depending on who you talk to. Personally, [by limited experience] I have found if 380/50 motors are run on 480V, 60Hz—they will naturally run at 6/5 overspeed, or a nonimal 4-pole indiction motor will run closer to 1800 rpm when intended to run around 1500 rpm. For fan duty, this usually results in an overload trip, as the motor is called to produce increased mechanical energy from electrical energy by virtue of raised line frequency. [Note some motors are designed as dual-rated and so marked on their nameplates.]

One other caution—if the 380V-primary transformer is connected to 480V, the nominal 220V secondary will now try to deliver around 278V, and that will often barbeque the transformer, usually along with a fair portion of the “220V” controls it serves.

Joined: Aug 2001
Posts: 7,520
TN-C existed in UK too I believe... Apparently, according to the ol' codger I served time under, this was the purpose of the little gap in the plugtop case next to the earth pin; to run a 'fly' to some convenient earth
I can't quite see how that could be the case. If you ran the system as TN-C right up to the wall outlet, then had a 3-pin socket, you'd just link neutral and earth at the socket, surely, just as Ranger explained above. Why would this system entail the use of a fly lead from the earth pin on the plug?

The little hole on British plugs for the earth pin is a curious feature though (or I should say "was" I suppose, as you don't find it on current plugs.

It seems more likely to me that it was provided simply as a convenient means for grounding to the house electrical system, e.g. to provide a signal earth for a radio.

Joined: May 2004
Posts: 186
Paul, I have some vague recolection when I was a pup being told that some buildings in the area were wired in the form as I now know as TN-C. If I remember correctly and it's a long time ago the installation was in M.I.C.C.
I think it was refered to as concentric cabling. Might be completely off beam here. Somebody tell me if I am!!

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