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chiller-man
17-05-2008, 10:10 PM
Does anybody have the problem we often have?
Our installation teams often report tripping ring main circuit breakers when pluging in a portable tool transformer, Most ring main MCB's are type B and the transformer obviously creates an initial surge, It would be better if the ring main MCB was a type C or D but inverably they are a B type. This problem is a real pain when you are carrying out an installation in an office or hospital clinic and take out all the computers.
So, My question is, Does anybody else suffer with this problem? and is there such a thing as a soft start transformer?

nike123
17-05-2008, 10:29 PM
Does anybody have the proble we often have?
Our instalation teams often report tripping ring main circuit breakers when pluging in a portable tool transformer, Most ring main MCB's are type B and the transformer obviously creates an initial surge, It would be better if the ring main MCB was a type C or D but inverably they are a B type. This problem is a real pain when you are carrying out an installation in an office or hospital clinic and take out all the computers.
So, My question is, Does anybody else suffer with this problem? and is there such a thing as a soft start transformer?


Portable tools are protected by double insulation and I don't see why it need to be on transformer except if you need different voltage then it is in sockets!
Or, is it some regulation on that matter in your country?
Use them without transformer or use battery powered tools if you are over-concerned about electric shock.
Double isolated tools could make bigger damage on your health when dropped on foot then if something go wrong with electrics (of course if they are mechanically undamaged).

chiller-man
17-05-2008, 10:35 PM
It is a safety regulation in U.K.
We use Hilti DD100 (110v) with 75mm diamond core bit, connected to a big 110v vacuum cleaner to collect dust, so the portable tool transformer has to be a 3Kva model.

monkey spanners
17-05-2008, 10:45 PM
I've had this happen with a 3kva transformer, had to turn everything off and plug in the transformer first before the other stuff on the circuit. This was to run my recovery machine.

chiller-man
17-05-2008, 11:02 PM
I thought about pluging the transformer into a lead with a plug on one end, a lighting dimmer in the middle and socket on the other end, plug the transformer into the trailing socket, make sure the dimmer is on low output, turn on the power and wind up the dimmer, once the dimmer is on max check the transformer output is 110v and away you go!
I need to try all this out, and possibly come up with a latching circuit so the dimmer is taken out of circuit once the transformer output is upto 110v.
Watch this space!

The Viking
17-05-2008, 11:18 PM
We used to get this with small transformers but we changed to slightly bigger and heavier transformers and the problem seems to have gone away...

nike123
17-05-2008, 11:44 PM
I thought about pluging the transformer into a lead with a plug on one end, a lighting dimmer in the middle and socket on the other end, plug the transformer into the trailing socket, make sure the dimmer is on low output, turn on the power and wind up the dimmer, once the dimmer is on max check the transformer output is 110v and away you go!
I need to try all this out, and possibly come up with a latching circuit so the dimmer is taken out of circuit once the transformer output is upto 110v.
Watch this space!


Just plug in some lamp when connecting transformer so that in moment of connection transformer to plug, secondary is not open circuit! That should prevent tripping of MCB!

chiller-man
17-05-2008, 11:52 PM
Interesting! So you are saying if there is a load connected to the secondary winding the transformer should not cause a surge and trip out the ring main circuit breaker?
If this works You have solved a real problem for us, Thanks Nike123, I will experiment with this idea.

Electrocoolman
18-05-2008, 01:54 AM
Portable tools are protected by double insulation and I don't see why it need to be on transformer except if you need different voltage then it is in sockets!
Or, is it some regulation on that matter in your country?


Hi Nike, ......just for info....
On UK building sites etc, our mains power has to be 110v and the transformer is in fact 55-0-55 with the centre tap taken to earth, for safety.
So most industrial power tools are 110v.....

Adrian

Electrocoolman
18-05-2008, 02:18 AM
Hi Chillerman,

The problem can arise when the transformer is a TOROIDIAL type construction. These are more compact than traditional types of transformers.

I've overcome this problem by connecting a NTC power thermistor in series with the transformer primary.

This gives a higher resistance which falls as its temperature increases, limiting surge current.

Google 'NTC Power Thermistor'

nike123
18-05-2008, 09:12 AM
Hi Nike, ......just for info....
On UK building sites etc, our mains power has to be 110v and the transformer is in fact 55-0-55 with the centre tap taken to earth, for safety.
So most industrial power tools are 110v.....

Adrian

Something like this?
http://tinyurl.com/5jvt4g

nike123
18-05-2008, 10:34 AM
Interesting! So you are saying if there is a load connected to the secondary winding the transformer should not cause a surge and trip out the ring main circuit breaker?


Small load, yes!

Sometimes helps, but if not, then you need to incorporate some inrush current limiting device.

http://tinyurl.com/6jyyzr
http://tinyurl.com/5wvlvg
http://tinyurl.com/65hd2t

If you do that with NTC, I would use, in your case, one of 40A in series with primary winding. Buy few of them and make connections inside transformer case with some terminals for easy changing.

chiller-man
18-05-2008, 05:27 PM
Thanks guys!

kiwireeferman
11-06-2008, 11:17 AM
Hi Nike, ......just for info....
On UK building sites etc, our mains power has to be 110v and the transformer is in fact 55-0-55 with the centre tap taken to earth, for safety.
So most industrial power tools are 110v.....

Adrian
Seems pretty crazy to me. I would think 110v would still kill you. Have these people never heard of RCDs or isolating tranformers.
Or is there some other reason for this regulation?

Electrocoolman
12-06-2008, 01:02 AM
Hi kiwireeferman

The transformers ARE isolating, with the secondary CT connected to earth. This gives 55v to earth, which is a lot safer than 110 or 240 to earth.

walden
12-06-2008, 10:35 AM
As always with things to do with the EU life is not clear. In order that Continental workers were not at a disadvantage if they worked in the UK, 230V, double insulated hand tools with RCD protection are allowed on British building sites.

On the Continent this arrangement is common and, I believe, it was Germany who complained to the appropriate EU committee to obtain this ruling so that its engineers would be able to use their own tools in the UK and not have to purchase or rent 110V tools and transformers.

nike123
12-06-2008, 11:38 AM
Hi kiwireeferman

The transformers ARE isolating, with the secondary CT connected to earth. This gives 55v to earth, which is a lot safer than 110 or 240 to earth.

They are not isolating if secondary is connected to earth.
They are for protection called:
PELV – Protective extra low voltage (http://en.wikipedia.org/wiki/Extra_low_voltage)

Isolation transformers are for SELV protection where we want the lack of a return path through earth (ground) that electrical current could take in case of contact with a human body, and therefore, they are not grounded on secondary side.

kiwireeferman
13-06-2008, 12:39 PM
When I was an apprentice and doing my electrical training a great game was putting your fingers across the terminals on a Variac to see how high you could wind the voltage up before you "chickened" out.