Confirming test on Siemens motor contactor coil failure....

If I connect the positive and neutral wires of standard 115 volt alternating house current to the below A1 and A2 terminals it would pull in the magnet, right ?

I ask as I have this model on a mill, that seems to have a burned out coil and the house current test was my only practical way to confirm...I'm more used to 24VDC coils where I have a DC test voltage generator......

I suppose somewhere I could buy just a new coil but suspect it would cost more than the whole NOS contactor from eBay, yes ?

Siemens 3TB42 12 A A8 NEMA Size Motor Starter 12 Volt Coil | eBay

Yes 115v on A1 and A2 should pull in the coil.

No great saving trying to get a replacement coil, just fit a new contactor.

Glad to see you cant type, and the contactor you are linking to has a 120v coil.

DM said:

Yes 115v on A1 and A2 should pull in the coil.

No great saving trying to get a replacement coil, just fit a new contactor.

Glad to see you cant type, and the contactor you are linking to has a 120v coil.

Click to expand...

Is UK 120 volts the same as USA 120 volts ? In other words, our 120 volts single phase is one positive 120 and one "neutral" plus a ground. Is UK 120 volts, two 60 volt positives and a ground....or is it the same as USA ?

To clarify further, if one checks USA voltage with a meter with ground probe on the green ground (or "earth" to you) wire and positive probe on the positive wire one will get 120 volt reading. But connect positive probe to neutral wire and one gets no voltage reading.

But with USA 240 volts single phase it is different.... for 240 volts there is no neutral...both wires are positive...each being 120 volts if measured individually with ground probe on ground wire.

Is UK the same or different ?

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Re "can't type"....I simply copied and pasted the URL from eBay...i.e. I didn't type that, the seller did.

But speaking of which, it is funny how many sellers of these will post 6 or more photos and give all sorts of info *except* the damn coil voltage ! The irony being that if new, I don't need ANY photos and ONLY need the model number and the coil voltage. And then some sellers almost show the coil voltage plastic tag but one can't quite make it out.... obviously most sellers of these have no clue what they actually have. Wonder what they cost new today ?

Milacron

"Is UK 120 volts the same as USA 120 volts ? In other words, our 120 volts single phase is one positive 120 and one "neutral" plus a ground. Is UK 120 volts, two 60 volt positives and a ground....or is it the same as USA ?"

Nearest we usualy have is from a 115V isolation transformer for building site use. centre tap on the 115v winding is connected to earth.

There are odd sites with a 115v supply that work the same way as your 120v system,(TNC-S, earth and neutral combined at the transformer but seperated when the service enters the property).

Our 240v system is usually (but not always) TNC-S where the only voltage you will measure between ground and neutral is the voltage drop on the neutral conductor.

Admin5 said:

Is UK 120 volts the same as USA 120 volts ? In other words, our 120 volts single phase is one positive 120 and one "neutral" plus a ground. Is UK 120 volts, two 60 volt positives and a ground....or is it the same as USA ?

Click to expand...

Not the same, no.

120 V (nominal) isn't even a majority / standard offering at all in the UK. Nor much of anywhere else outside of North America or Japan.

An (Earthed) Centre-tap to Neutral is displaced upward another "layer" vs US practice. See also Canadian system.

'Translate' as if the UK / international wall-outlet was one leg to Neutral off a US-spec 4-wire 416 VAC Wye or 480 VAC 5-wire Delta AND NOT their 208/240 VAC versions.

Safer assumption if you have to work with it outside the US.

Been covered. On PM, even.

On-edit: DM types faster. Or pauses less for coffee. The 'jobsite' locally-Earthed CT transformers are lovely. Same-again on US nominal 120 or Japanese nominal 100 can be even safer yet.


Bill

Monarchist said:

Not the same, no.

120 V (nominal) isn't even a majority / standard offering at all in the UK. Nor much of anywhere else outside of North America or Japan.

An (Earthed) Centre-tap to Neutral is displaced upward another "layer" vs US practice. See also Canadian system.

'Translate' as if the UK / international wall-outlet was one leg to Neutral off a US-spec 4-wire 416 VAC Wye or 480 VAC 5-wire Delta AND NOT their 208/240 VAC versions.

Safer assumption if you have to work with it outside the US.

Been covered. On PM, even.

On-edit: DM types faster. Or pauses less for coffee. The 'jobsite' locally-Earthed CT transformers are lovely. Same-again on US nominal 120 or Japanese nominal 100 can be even safer yet.


Bill

Click to expand...

OK but the bottom line is even with USA style 120 house current voltage, the test I did should have activated the magnet coil of the motor contactor, if the coil was good....yes ?

If a voltmeter connected to the two wires reads 120 nominal volts, then that's what you have 120 volts. Whether one wire is grounded or derived makes no difference. On thing you have to be careful of is that the UK is 50 Hz, US is 60 Hz. If you are buying something to go where there is 50 Hz, make sure the magnetics are rated 50/60 Hz.

Another note about IEC contactors, in the small sizes the coils are not normally replaceable like in the US. Replaceable? Yes, if you can find a coil and disassemble the contactor.

Tom

Did you do a continuity test with an ohmmeter?

Bill

Milacron said:

OK but the bottom line is even with USA style 120 house current voltage, the test I did should have activated the magnet coil of the motor contactor, if the coil was good....yes ?

Click to expand...

Certainly. So long as you had enough current available.

As-in, not ALL control transformers will drive ALL coil loads.

Not really a factor for direct off-the-line testing. I only mention it as it is my personal pref to work with some such means of isolation (and fuse and/or CB) whenever practical.

Less "shock and awe" when, not if, I get tired or careless and screw the pooch.

Well, if the coil was OPEN, the application of 120V would not produce the desired effect. But if the coil was SHORTED, it might blow your circuit breaker or melt whatever little wires you used to make the connection. That's just a slight admonition as to your test methodology...

That series of product is long obsolete with Siemens, so coils are going to be harder to find, translate: $$$
in addition, those were not really designed to be replaced, in the IEC world where that came from if the coil is dead, most likely the contacts are worn out too. Their design concept is to never replace things like coils and contacts. So yes, it's going to be cheaper and easier to just swap it out with a new one.

9100 said:

Did you do a continuity test with an ohmmeter?

Bill

Click to expand...

That would be my first test.

Jraef said:

Their design concept is to never replace things like coils and contacts. So yes, it's going to be cheaper and easier to just swap it out with a new one.

Click to expand...

Not so true. Allen Bradley sells contact kits which are available for the ESP100 line.

rons said:

Not so true. Allen Bradley sells contact kits which are available for the ESP100 line.

Click to expand...

Note that both jraef and myself said IEC. AB and others have hybridized the IEC concept to be somewhat serviceable.

When I was working for GE in the early 1980's, the company was developing a completely new line of industrial control, the 400 Line. It was to be an international product to service all markets. Only 18.5 KW and above had replacement coils and contacts. The smaller ones were considered to be throw away.

Tom

If a 120 volt AC coil of course it should. Variety of grounds to earth and tap methods don't matter. 50HZ vs 60 should still pull in.
But the first check is always .....Ohmm....ohmm . ohms before you stick power in with lord knows what for fuses in the line.
Assume you have already made sure it is not mechanically stuck by shoving it in by hand with a screw driver and that is bounces back and forth freely.
Bob

rons said:

Not so true. Allen Bradley sells contact kits which are available for the ESP100 line.

Click to expand...

Well, ESP100 is an old obsolete solid state overload sold by Furnas (now Siemens), but I know what you were getting at.

Yes, companies that sell IEC components here in the US are basically obliged, by virtue of market demand, to sell the replacement parts for them. But years ago when I worked for Klockner Moeller, the Germans I worked for derided us based in the US all the time for this concept. The European way, and by virtue of that the design concept, was to never bother with the time and effort it takes to take a cheap little contactor apart to replace a coil or contacts if they fail. They KNEW, even back then in the 70s, that it was far far cheaper to just replace it.

Coils were sold here in the US mainly because people were constantly ordering the wrong coil voltage and had to change it. But when I first started in 1978, they didn't even OFFER replacement contact kits. It was only under pressure from North American distributors that they bothered to come up with them. In the case of smaller size contactors, it forced them to redesign the entire product line because the smallest sizes were a "clam shell" design, split down the middle vertically. If you tried to open the case to replace contacts, the springs shot out and bounced all over the place. Siemens, S+S, Telemecanique, Asea, they were all like that at the time.

I remember them days!

Tom

Jraef said:

...

Yes, companies that sell IEC components here in the US are basically obliged, by virtue of market demand, to sell the replacement parts for them. But years ago when I worked for Klockner Moeller, the Germans I worked for derided us based in the US all the time for this concept. The European way, and by virtue of that the design concept, was to never bother with the time and effort it takes to take a cheap little contactor apart to replace a coil or contacts if they fail. They KNEW, even back then in the 70s, that it was far far cheaper to just replace it....

Click to expand...

The other half of that policy is because the IEC stuff has wildly varying ratings, depending on load and load type. There are something like 70+ fairly common load types, and a contactor may have different ratings for each. They tend to approach the selection process as an engineering task to find the smallest and cheapest part that will work, usually a task requiring a "Dipl. Ingeneiur" (PE).

The US approach is to use a standard UL sized contactor for the motor load and be done, a task any industrial electrician can accomplish. The contactors tend to be heavier duty, and worth repairing, plus they are made to have coils replaced to cover different voltages.

JST said:

The other half of that policy is because the IEC stuff has wildly varying ratings, depending on load and load type. There are something like 70+ fairly common load types, and a contactor may have different ratings for each. They tend to approach the selection process as an engineering task to find the smallest and cheapest part that will work, usually a task requiring a "Dipl. Ingeneiur" (PE).

The US approach is to use a standard UL sized contactor for the motor load and be done, a task any industrial electrician can accomplish. The contactors tend to be heavier duty, and worth repairing, plus they are made to have coils replaced to cover different voltages.

Click to expand...

That's right on. The way the people at KM explained it to me is that after WWII, the men that survived had to go back to work immediately, so nobody had time for anything new. But the next generation, the ones that were kids during the war, took full advantage of the Marshall Plan to get 4 year degrees in Engineering; nobody wanted to be electricians any more because tradesmen were the first to get pulled into the previous two wars. So in the late 50s they were awash in degreed Engineers, but few electricians. At the same time, material shortages meant everything was a lot more expensive, especially stuff like silver for contacts. So for them, it was less expensive to have an EE spend an hour "rationalizing" every detail of a machine motor and control application and use JUST ENOUGH contactor to do the job, no waste. Part of that "rationalization" process involved the exact amount of time they expected everything to last, from the electrical parts to the mechanical parts, all built as close to the bone as possible. So if the machine was going to wear out at 1 million operations, why bother having a set of contacts that will out last it? And since there were so few electricians, they didn't want them sitting at a bench pulling apart a component that will not be useful for very much longer anyway, so it was all designed for "rip and replace".

At the same time here in North America, Engineers were in an ivory tower somewhere, paid too well, while tradesman like electricians were being churned out of trade schools like crazy as returning soldiers looked for something to do, so they worked relatively cheaper. Factories were growing so fast that nobody had time to "rationalize" every little detail either. So the parts were designed to last a lot longer than the machine might so they could be re-used after a factory change, and selected in a way that an average electrician could chose a part on his own that would be able to handle the worst thing they could throw at it, then repair it 4 or 5 times.

Both you are right on! The only item is that the American practice predated WWII. Of course, before WWII, everything was repairable, even car batteries.

Tom

CarbideBob said:

If a 120 volt AC coil of course it should. Variety of grounds to earth and tap methods don't matter. 50HZ vs 60 should still pull in.
But the first check is always .....Ohmm....ohmm . ohms before you stick power in with lord knows what for fuses in the line.
Assume you have already made sure it is not mechanically stuck by shoving it in by hand with a screw driver and that is bounces back and forth freely.
Bob

Click to expand...

As it already had power to its coil in the machine before removal I knew it was safe to power it offline. And yes, moves freely, not stuck, can activate it by hand by pressing it's button on the front.