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Topic Title: STR38 S M25 N1 merlin gerin breaker
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Created On: 20 January 2013 09:37 AM
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 20 January 2013 09:37 AM
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BESATSAKEN

Posts: 6
Joined: 20 January 2013

Hello fellow electrical practitioners:

I would like to post a problem on my merlin gerin breaker which rondamly trips during start of its pump load. the trip indication is always earthfault. I made insulation tests of the pumps (2 line pumps rated 7.5hp and 1 supply pump rated 60hp) and found them good with all in Giga ohms. Likewise the insulation resistance of the cables from the breaker to load is good at Giga ohms. The pumps have MCC and during the start of any pump, the merlin gerin breaker trips and no trip occurs at the MCC individual breaker. During one time the pumps are set to run, i set-up 1 clampmeter on the neutral cable to check if there is an abnormal spike during starting. I found no rise at all on the current (4 Amp but the setting for earthfault is 500 A) but there is an earth fault trip. Could it be possible that i have a nuisance tripping. I am suspecting now the merlin gerin breaker as the problem.
 20 January 2013 10:44 AM
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dlane

Posts: 690
Joined: 28 September 2007

Hi and welcome to the forums.

Are all of these pumps direct on line or star delta started or are there variable frequency drives involved. VFDs can introduce harmonics into earth circuits and cause spurious tripping.

Instead of a clampmeter I would be more inclined to install an energy analyser for a period of time that would measure harmonics and then study that data.

Is this an actual earth fault trip or a restricted earth fault trip as they mean different things. Do you also know what the arrangement of the earth fault protection is, such as single current transformer, core balance, residual current or voltage shunt trip. Knowing the arrangement will give you ideas of different faults to look for.

Depending on your setup and your type of breaker you can either get a bespoke test unit from Schneider, usually when the protection is built into the breaker, or you can use a standard injection test set to test the operation and sensitivity of the protection system.

I have also come across mechanical issues on some Schneider breakers that cause them to spuriously trip and slowly get worse as more tripping occurs until you can't actually reset them. This was a fully enclosed MCCB type.

You may also want to consider moving the post over to the Energy forum as there may be people on there more familiar with breakers and motor supplies that may not frequent this forum.

Kind regards

Donald Lane
 20 January 2013 11:39 AM
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BESATSAKEN

Posts: 6
Joined: 20 January 2013

The 3 pumps are each in direct on line starter; there are no VFD eqpt, there have been no added equipment since the breaker was installed in 1993 (almost 20 yrs.now). Due to limitations of our testing device, this clampmeter is the one available. Its an actual eartfault using a single neutral core CT connected from the neutral of the transformer.

Thank you of your reply.

Besat
 20 January 2013 01:31 PM
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IanDarney

Posts: 32
Joined: 18 January 2003

I had the same sort of problem with the motor start circuitry for the Consub submersible. It was a
switch-on surge due to high value of capacitance between the supply conductors and the 'earthed' conductors of the structure. You can observe this surge by fitting a clamp-on current monitor transformer round ALL the live power conductors. DC checks tell you very little.

You can contact me at iandarney@blueyonder.co.uk.

Ian Darney
 05 February 2013 01:02 PM
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sil9090

Posts: 4
Joined: 21 January 2013

Hi
the nuisance tripping problem is well documented and the cause of the malfunction has been blamed by manufacturer on numerous cause, one being a fungal growth on components and another on end of life component failure.
I have been on site when a known faulty STR has been tested using Merlin Gerin secondary test set and primary injection.
The device tested out perfectly ,only to trip 2 hours later for no apparent reason.
The STR protection unit can be replaced by Schneider for around £1864 net and £1200 labour net including costs making a total cost of over £3000 net.Or you could retro fit NW with micrologic protection (hope you have deep pockets).
Or you could fit a replacement digital 21st century replacement protection unit that is a direct fit onto your breaker using the same wiring and connections as well as the same fixings.
I have experience of these units and once fitted your nuisance tripping problems will be over.
These people also offer full support for your Masterpact M ACB's.
Link removed
Link removed
Link removed
Regards
Peter
 05 February 2013 01:08 PM
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sil9090

Posts: 4
Joined: 21 January 2013

Hi
I gave you 3 links but the site removed these so just put nuisance tripping Merlin Gerin str38s into your search engine.
Regards
Pete
 05 February 2013 08:59 PM
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davidwalker2

Posts: 194
Joined: 29 April 2009

Have a look at the 'nuisance tripping' strand on the Energy Forum. Others have this problem!

David
 05 October 2013 02:33 AM
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tigert

Posts: 2
Joined: 13 July 2009

Maybe you will prefer the spare parts for the Merlin Gerin Masterpact air circuit breaker.
For more information,please mail to wlxydq@163.com
We served the Merlin Gerin Masterpact ACB breaker for 15 years.
 10 October 2013 11:58 AM
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tigert

Posts: 2
Joined: 13 July 2009

STR38S's normal age is 15 to 20 years.
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