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I have just completed an installation on a fruit farm which all tested 100%.
There are 3 x 3 phase pumps 32a 41a & 41a, only 2 run together at an one time. When the second pump is started the 100A 100mA trips out.
The pumps are run from variable speed controllers on a three wire system, no neutral.
All the equipment is from one supplier. They want to remove the RCD and replace with a main switch but as it is a horticultural installation I feel this is the wrong route. Harmonics may be an issue but I would assume the supplier would be aware of this.

Any ideas welcome.
 
if there's no livestock present, try a 300mA RCD.
 
VSD’s have inherent leakage. Try a 300mA RCD or put each pump on its own. You should have harmonic filtering in place.
 
If you owned an earth leakage clamp, you would have an idea of the value of the leakage current that is tripping the existing RCD. Then you could determine if a 300mA or 500mA RCD would fulfill your requirement. Not forgetting of course the use of S type (time delay) RCD's...
 
Why S type?

Well, we don't know what the leakage is that is presently taking out the 100mA unit, ...if it's a high short duration current, then a 300/500mA may still not suffice. Only really mentioned S type to keep in mind as an alternative. Even with timed delayed RCD's, we are still in the realms of mSec'....
 
If you owned an earth leakage clamp, you would have an idea of the value of the leakage current that is tripping the existing RCD. Then you could determine if a 300mA or 500mA RCD would fulfill your requirement. Not forgetting of course the use of S type (time delay) RCD's...

Although I totally agree with you , the op will be limited to a maximum of 300mA in order to comply with 705.411.1 (iii)
 
As Tony says VFD's have inherrently high standing leakage and many VFD manufacturers caution against supplying via RCD's. I doubt a time delayed RCD will help you in this scenario because most of the leakage is a result of the VFD's internal filters that clean up the waveform that supplies the motor so ironically the better the VFD and the better the internal filtering the worse the leakage usually is.
 
Why this set up requires EL protection is beyond me.

Three off pump sets and associated control gear is going to be a fixed installation in a plant room.
 
Yeah, I'm hesitant to comment on the RCD requirements because I don't work to and don't know the UK regs. Under normal circumstances we wouldn't install this kind of set up with an RCD supply for exactly the reasons highlighted in the OP.
 
And the equipment supplier wants to remove the RCD. I seem to recall the equipment requirements take president.

This is one of those situations where you need to see the site to make a decision.
I’ve never had to do it under BS7671 but under M&Q you can designate an area to be outside the general scope of the regulations. IE the plant room isn’t horticultural, it’s commercial.

Large commercial outfits couldn’t function without such a get out.
 
The requirements of the regulations are pretty clear for once.
Socket outlets up to 32A - 30mA RCD
Socket outlets above 32A - 100mA RCD
All other circuits - 300mA RCD (S type permitted if necessary)

But of course the designer of the installation can use his knowledge experience and professional judgement to design an installation outside of the regulations if it is necessary.

Now if the normal operation of the equipment produces high residual currents then I would suggest it is time to take a common sense approach to the design and replace those RCDs with a more sensible means of protection.
The RCD is there primarily for the prevention of fire, maybe make an assessment of the likelihood of a fire resulting from an electrical fault in the location. As Tony said if it is in a dedicated plant room it could be considered to be outside of the normal horticultural installation.
 
The requirements of the regulations are pretty clear for once.
Socket outlets up to 32A - 30mA RCD
Socket outlets above 32A - 100mA RCD
All other circuits - 300mA RCD (S type permitted if necessary)
Are these defined in BS7671? Assuming the VFD'sare part of the pump control system, not part of the actual electrical supply wouldn't they fall outside the jurisdiction of 7671? Our installation regs would only cover the circuit to the isolator or socket point, what happens after that is under the scope of different regs.

Now if the normal operation of the equipment produces high residual currents then I would suggest it is time to take a common sense approach to the design and replace those RCDs with a more sensible means of protection.
The RCD is there primarily for the prevention of fire, .......
I'm not sure about RCD's being specified as fire protection, we'd only ever specify them as a means of achieving disconnect times in the case of a fault or as protection against lethal shock for a user who's not electrically competent.
 
Are these defined in BS7671? Assuming the VFD'sare part of the pump control system, not part of the actual electrical supply wouldn't they fall outside the jurisdiction of 7671? Our installation regs would only cover the circuit to the isolator or socket point, what happens after that is under the scope of different regs.


I'm not sure about RCD's being specified as fire protection, we'd only ever specify them as a means of achieving disconnect times in the case of a fault or as protection against lethal shock for a user who's not electrically competent.

Yes the control system will pretty much fall outside of 7671, but the supply to the isolator does fall under 7671. And as such it falls under 'all other circuits - RCD 300mA.

And yes 7671 does stipulate that 300mA RCDs are to be used for protection against fire!
Don't I ask me how though, I always thought installing things properly with some common sense to where you locate everything and putting connections in non-flammable enclosures would protect against the wiring starting fires.
 
Weird but every day's a school day, I've never seen RCD's specified with fire prevention in mind. They're not good at picking up arcing faults which is a common cause of fires, why not specify an AFCI type device in that case, it would be a better tool for the job.
 
I couldn't understand it when I was an apprentice, the college lecturers couldn't give a good answer and my mentor was of the opinion that you install things to a high standard and avoid connections in areas of particular flammability and generally do a good job.
Prevention is always better than cure, especially when the supposed cure is reliance on a damned RCD
 
Weird but every day's a school day, I've never seen RCD's specified with fire prevention in mind. They're not good at picking up arcing faults which is a common cause of fires, why not specify an AFCI type device in that case, it would be a better tool for the job.

The way I have looked at it is that short circuits generally occur in equipment and may be contained by the equipment (cable penetrations not withstanding). Faults to earth can easily occur outside or at the edge of equipment so faults to earth are more likely (perhaps) to be a problem for fire risk and if you have an RCD then the fault current is much lower and less likely to cause a fire risk from arcing.
 
Weird but every day's a school day, I've never seen RCD's specified with fire prevention in mind. They're not good at picking up arcing faults which is a common cause of fires, why not specify an AFCI type device in that case, it would be a better tool for the job.



Not according to many Electrical Engineers in the States, many of which are calling them a useless gimmick. Personally i don't know enough about them, to make a judgement, nore am i aware of the means/method of testing these arc sensing breakers. From what i have read though, these units are bloody expensive, especially the combined arc fault/rcd breakers!! lol!!
 

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