TWO PHASE MOTOR

[SUNRAY]

Where?

2 conversations from an American co-worker of Seattle origin:
Within hours of starting work in UK - How come not many people get hurt on your dangerous high voltage supply?
By the end of a couple of months - "Your supplies don't fluctuate much."
"How much do they back home?"
"Lots, from 90 to 115. Sometimes lower in the summer."
"I thought it's 120."
"Yeah right."

 

[SUNRAY]

There maybe no grounded Neutral to the appliance.

Why?

 

[JohnW2]

Why?

I think what bernard was probably suggesting was that a 'Class II' 110V tool/appliance could be supplied (with a 2-core cable) from the two "55s" of a 55-0-55V transformer. In that situation, the tool/whatever would obviously only see a 'single-phase' 110V supply between the two conductors supplying it, and the fact that the centre tap of transformer was connected to earth would have no effect on that - the only effect of that earthed centre-tap would be that the two conductors supplying the load were only at 55V relative to earth ('earth' being something that an {intact} Class II load knows nothing about).

Kind Regards, John

 

[SUNRAY]

I think what bernard was probably suggesting was that a 'Class II' 110V tool/appliance could be supplied (with a 2-core cable) from the two "55s" of a 55-0-55V transformer. In that situation, the tool/whatever would obviously only see a 'single-phase' 110V supply between the two conductors supplying it, and the fact that the centre tap of transformer was connected to earth would have no effect on that - the only effect of that earthed centre-tap would be that the two conductors supplying the load were only at 55V relative to earth ('earth' being something that an {intact} Class II load knows nothing about).

Kind Regards, John

I wasn't sure whether the comment meant:
A grounded Neutral to the appliance is not permissable.
Or
There may or may not be a grounded Neutral to the appliance.

The main reasons I asked the question:
1) All 3 of the powered tools provided in a kit for splicing fibre optics ran on a centre tapped transformer. Actually it was a 120V primary: 58-0-58V secondary of U.S. origin. This kit would typically be powered by a 110 generator or yellow transformer. 2 of the tools stopped working when the centre tap/earth wire in the transformer broke, as part of the repair process I measured the current of all 3 conductors of one tool which was something near 1A on both hots and 100mA on neutral
2) Most, if not all, of the lead lamps I used within BT contained 50V bulbs and ran either on CB or half of a 110V transformer.

 

[bernardgreen]

The motor is in America
-------------------------
The power source in America is a centre tapped secondary winding on a transformer which from end to end is 220 volts. 110--0--110 P1--N--P2
The N ( centre tap ) is grounded and is refered to as supply Neutral.

The load ( the motor ) needs 220 volts to operate.
The motor is therefore connected as L1 to P1 and L2 to P2.
The motor does not require the N from the supply but probably does have a terminal on which the N can be parked
(edit see next post about a possible safety function of the grounded centre tap )

Motor emigrates to the UK
------------------------------
The power source in the UK is a secondary winding on a transformer which from end to end is 230 volts. 0--230 N--P1
N ( one end of the winding ) is grounded and is refered to as supply Neutral.

The motor still needs 220 volts to operate
The motor is therefore connected as L1 to P1 and L2 to N
The motor does require the N from the supply but it has to be connected to L2

 

[bernardgreen]

2 of the tools stopped working when the centre tap/earth wire in the transformer broke,

These tools might have had 58 volt control circuitry supplied by one phase and the Neutral and without that 58 supply to the control the device could not operate. It cpuld even be a safety function that the tool would not operate if the centre tap / earth was missing.

It might be possible that the 110--N--110 motor has a similar safety feature that does require the grounded centre tap to be connected.

 

[ericmark]

I remember (1970's) working for the county council on portable traffic lights, they had just brought out vehicle sensed traffic lights, with microwave detectors (RADAR) to see when a car was waiting, they came supplied with Peak RADAR however these were proving too sensitive and waving trees were setting off the traffic lights, so they were changed for Mullard and I fitted the new heads, tested in the depot, and all worked A1, took to the site, and they did not work when powered from generator, returned to depot and all A1.

As a young lad I was baffled as to why OK in depot, but failed on site, some phone calls and it turned out the Mullard actually used the centre tap of the 110 volt supply, and the generators did not have a centre tap, so I had to fit a auto transformer to generate the centre tap, talking to my boss he said that's no good, it should not use any power from centre tap, as if the 7 core cable is damaged then it can make the traffic light head live to 55 volt, and it only takes 25 volt to kill a cow.

So the auto transformer needed fitting in the heads, all the Mullard heads were returned and modified. This of course is still the case, TN-C is very limited as to where it can be used, so even if we have centre tap, unless using 4 core cable, we can't use the centre tap.

As to using a 400 volt supply (2 phase) yes have seen many times 400 to 230 volt transformers used because there is no neutral supplied to the machine, I have never seen with split phase (460 volt) a transformer used to step down to 230 volt, always used one phase. I think for a domestic supply (to a premises in the charge of an ordinary person) one is limited to 125 amp, in real terms 100 amp, so if the user needs more than 100 amp, then need to have multi supplies, be it two or three phases, or split phase, would depend on local supply and transformer, so common to find a farm with split phase supply one to farm buildings and one to house. You can have a domestic 3 phase supply with 100 amp per phase, but not a 300 amp supply, as you need type tested distribution units called consumer units which can't be over 125 amp each. I have fitted a three phase switched fuse with 3 x 100 amp fuses, one to each of three consumer units, and all three fuses came off same supply, not sure if this complied?

However other than using a capacitor to start, not seen a two phase motor, and since twin supplies in this country are often split phase rather than two phases from a three phase supply, to build a machine using a two phase motor would be asking for problems.

 

[JohnW2]

I wasn't sure whether the comment meant:
A grounded Neutral to the appliance is not permissable. ... Or ... There may or may not be a grounded Neutral to the appliance.

The English language can be a pain at times! I have to say that, at the time, The first of those possible meanings did not even occur to me - and I still think that it's pretty unlikley that such was the intended meaning!

In view of this potential ambiguity, I try to avoid using the word "may" (alone), particularly in 'formal' writing. Instead, for that former meaning I would probably write "is permitted to" or "is allowed to", whereas for the latter meaning I would probably use "may possibly"/"possibly may" or (even if/when possibly/probably grammatically incorrect!) "might"/"possibly might"/"might possibly"!

Kind Regards, John

 

[winston1]

The motor is in America
-------------------------
The power source in America is a centre tapped secondary winding on a transformer which from end to end is 220 volts. 110--0--110 P1--N--P2
The N ( centre tap ) is grounded and is refered to as supply Neutral.

The load ( the motor ) needs 220 volts to operate.
The motor is therefore connected as L1 to P1 and L2 to P2.
The motor does not require the N from the supply but probably does have a terminal on which the N can be parked
(edit see next post about a possible safety function of the grounded centre tap )

Motor emigrates to the UK
------------------------------
The power source in the UK is a secondary winding on a transformer which from end to end is 230 volts. 0--230 N--P1
N ( one end of the winding ) is grounded and is refered to as supply Neutral.

The motor still needs 220 volts to operate
The motor is therefore connected as L1 to P1 and L2 to N
The motor does require the N from the supply but it has to be connected to L2

Why do you continue to propagate this myth that the US supply is 110/220v? It is not. It is 120/240v plus or minus 5%. 110/220 is well outside those limits.

 

[ericmark]

Why do you continue to propagate this myth that the US supply is 110/220v? It is not. It is 120/240v plus or minus 5%. 110/220 is well outside those limits.

Why do you continue to believe the myth that US supply has same volt drop as UK, if you had read the replies to this post it is clear due to volt drop US supply is rarely 110 never mind 120 volt.

I had same problem in Algeria, standard supply was 110 volt, and across two phases down to 180 volt with no volt drop, with volt drop even less, so a Dutch air conditioning unit would repeated stall when it tried to start and would burn out the thermal cut out. I had a devils own job to convince the bosses that one could not use a 220 volt AC across two phases, I had to get a company director to read meter to convince the bosses that it was well under 180 volt.

 

[JohnW2]

Why do you continue to believe the myth that US supply has same volt drop as UK, if you had read the replies to this post it is clear due to volt drop US supply is rarely 110 never mind 120 volt.

To be fair, I assume winston was talking about nominal supply voltages, not the voltages at the end of final circuits due to VD within the installation, and I believe that it is indeed true that the nominal supply voltage in North America is 120V±5%.

As far as I can make out, the US recommendations for maximum VD withing installations are generally smaller (2%-3%) than thsoe we see in the UK.

Kind Regards, John

 

[winston1]

Why do you continue to believe the myth that US supply has same volt drop as UK, if you had read the replies to this post it is clear due to volt drop US supply is rarely 110 never mind 120 volt.

I never said or implied that. When ever I have measured US voltage on odd trips there it has been 120 to 123V.

 

[bernardgreen]

To be fair, I assume winston was talking about nominal supply voltages,

I don't think Winston does "nominals"

If the can ( literally a tin can transformer ) is labeleld "120 V" then 120 V is what it provides, even if the 11kV supply to it is down about 9 kV

I do now recall one paging transmitter site that had motor driven "Variacs" to automatically compensate for the variations in the voltage drop in the supply network.

When ever I have measured US voltage on odd trips there it has been 120 to 123V.

Who takes a volt meter on odd trips. Or did Winston go to the US with a complete tool kit for some emgineering work out there ?

 

[winston1]

Who takes a volt meter on odd trips.

One of these is very useful when travelling.

https://www.banggood.com/DM551-AC-8...eter-Voltmeter-p-929140.html?cur_warehouse=CN

 

[JohnW2]

I don't think Winston does "nominals"

True, but I think he does 'permissible ranges'. I think he accepts that the permitted range of supply voltages in the UK is 216.2V to 253V, and although he disagrees about "what that is called", it's at least true that both of the options 'being considered' ("230V" and "240V") are well within that 'permitted range', so it really does become just a terminological/semantic issue.

However, as I understand it, in North America the 'permitted range' is 114V - 126V and, as he rightly says, 110V is not even within that range - seemingly making it far less appropriate/reasonable to call that supply "110V".

Kind Regards, John