Phase Protection

[Khonwan]

I have a Thai friend who is a learned-on-the-job electrician. He recently installed a control box for my new borehole 3-ph 2hp submersible pump. As can be seen in the photograph, it contains a phase protector and a contactor coupled with a thermal overload relay.

Having just had him rewind a 3-ph 3hp motor (nothing to do with the borehole) after it being damaged due to a dropped phase when one fuse in a cut-off went, he advised me to buy a similar phase protector, contactor, and thermal overload relay, which I did. I was going to install these myself today but I am now thinking that I should return the contactor and thermal overload relay to Global House (within their 30 days refund guarantee). It seems to me that the phase protector should be sufficient by itself, though I’m happy to install them if of any benefit.

To fit or not to fit, that’s the question.

[Khonwan]

I found the answer via a wiring diagram I hadn’t noticed: fit!

[InterestedObserver]

Loss of phase / phase reversal / phase unbalance protection and a thermal overload relay are not the same thing. If you are serious about protecting three-phase equipment you should have both.

[electau]

Phase failure, phase voltage imbalance, phase rotation, under and over % voltage protection can be obtained by using separate relays or a relay that combines all functions. 3 phase and 3 phase and N.

Available as plug in units on a base or wired. DIN rail mounting. The voltage free NC/NO contact(s) are connected in series in the control wiring to the motor contactor.

Thermal protection of the motor is obtained by an overcurrent relay set to the motor FLA, the motor current is through the elements of the relay and the NC/NO contact again is connected in series with the control circuit. The contacts will open under overload conditions and in the case of a 3 phase motor overcurrent conditions caused by loss of phase ( known as single phasing) Unit is fitted to the contactor.

The PFR should be protected by 3 x1 pole 6A or 10A MCBs

If you have single phase 220V you may only require under and over % voltage protection, as if one has loss of supply the motor will not run and phase rotation will not be affected.

Phase failure protects from loss of supply on one phase. Phase rotation protects from damage which could be caused by inadvertant reversal of two phases ( submersible pumps, compressors etc) and voltage protection % from under and over voltage eg 20% under 10% over from normal supply volts.

Edited October 27, 2010 by electau

[InterestedObserver]

The W-OP4 Protection Relay included in the OPs installation does not include phase sequence sensing . A W-PR3 with phase sequence protection may have been more appropriate. Depends if the 3-phase submersible pump will be damaged, or even pump, with reverse rotation. I also note that the L3 and N terminals are connected together, that should be investigated further for proper functioning of the relay.

Edited October 28, 2010 by InterestedObserver

[Khonwan]

The W-OP4 Protection Relay included in the OPs installation does not include phase sequence sensing . A W-PR3 with phase sequence protection may have been more appropriate. Depends if the 3-phase submersible pump will be damaged, or even pump, with reverse rotation. I also note that the L3 and N terminals are connected together, that should be investigated further for proper functioning of the relay.

I’m not quite sure where you see L3 linked to N. I suspect you refer to the link on top of the phase protector between L3 and 11. If so, then this is in accordance with the wiring diagram that came with the phase protector.

[InterestedObserver]

If that is in fact terminal 11 instead of terminal N then you are correct. The diagram on the internet has the terminals along the top as L1, L2, L3, N and 11. You must have the 3-phase, 3-wire version of the relay hence different terminal markings.

.

Edited October 28, 2010 by InterestedObserver

[Khonwan]

I have the 3 phase 4 wire (3P4W – code 6006) version but it is slightly different from that depicted on the WIP website. L1,L2,L3,11,21 on top and 12,14,22,24,N on bottom in the case of my version. The website shows L1,L2,L3,N,11 on top and 12,13,21,22,23 on bottom. I’ve spotted a number of errors in their website – I hope this product is of better quality than their website.

[InterestedObserver]

I hope the submersible pump is properly grounded. Not a green wire to be seen anywhere in the starter panel.

[electau]

L1,L2,L3 and N are the supply to the PFR.

NC/NO contacts for the control circuit are 11,12,13 and 21,22,23.

The 220V control circuit voltage for the contactor is taken from one of the phase terminals in this case L3. the neutral to N.

The pump should be earthed and also the metal switchboard enclosure.

[Naam]

my setup:

[Khonwan]

No, the pump is not earthed. I had already sunk a ground rod but the contractor installed the pump using a 3-core cable. I ended up using the rod to ground my neutral overhead cable as part of my MEN system.

However...the pump is due to be raised within the next few days by the contractor to resolve a blockage so I will take the opportunity to earth it (and the control box!).

I presume that the one ground rod can be used for earthing the pump and as a MEN.

[InterestedObserver]

If you only have a 3-core electrical cable and a steel pipe with screwed joints leading to the submersible pump, I'd be tempted to use the steel pipe as the grounding (earthing) conductor. Just connect the steel water pipe to the ground rod using approved grounding clamps and cable.

Edited October 29, 2010 by InterestedObserver

[Khonwan]

PVC pipe - but as I mentioned, the pump must be raised in any case since it isn’t working (it’s blocked) so it will cost very little to add a 90m single core earth cable.

[InterestedObserver]

PVC pipe - but as I mentioned, the pump must be raised in any case since it isn't working (it's blocked) so it will cost very little to add a 90m single core earth cable.

The 3-phase submersible pump isn't working (it's blocked)! Maybe the pump is turning the wrong way, try reversing the phase rotation.

Edited October 29, 2010 by InterestedObserver

[Khonwan]

Unfortunately not. I witnessed the pump delivering a great output for all of 2 minutes before petering out. It’s a new borehole that was left for a few weeks awaiting delivery of a pump – this was its first trial. Not a great start after spending 180,000 baht.

[electau]

No, the pump is not earthed. I had already sunk a ground rod but the contractor installed the pump using a 3-core cable. I ended up using the rod to ground my neutral overhead cable as part of my MEN system.

However...the pump is due to be raised within the next few days by the contractor to resolve a blockage so I will take the opportunity to earth it (and the control box!).

I presume that the one ground rod can be used for earthing the pump and as a MEN.

The PE (protective earth) is run from the motor to the main switchboard earthing bar, the ME (main earth) is run from the main earthing bar to the electrode, the MEN connection between the main neutral link and the earth bar.

It would be recommended that you fit RCD protection to the pump circuit.

[Khonwan]

The borehole is 330m from the house 'as the crow flies'. It would not, in my opinion, be sensible to run an earth to the CU there – much safer to earth it at the borehole. Also, the house CU is single phase whilst the pump is 3-phase (as mentioned).

My main house is serviced by one phase (currently) where the CU has now been fitted with an RCD(RCBO) and the earth bus linked to the neutral on the supply side of the RCD. My situation is slightly different from the average forum member, however, in that I have a large farm with 8,000m of overhead cable;1500m between main breaker and my 3-phase transformer; earthed neutrals approximately every 200m.

I can’t see any purpose in an RCD (which, in this case would have to be 3-phase RCD) in the case of a motor located 80m underground with no metal between it and the surface (other than the double insulated copper electrodes). In fact I can’t see a strong case for even grounding it, though am willing to do so if the contractor has to raise it anyway to clear the blockage I mentioned. It seems to me that a 90m ‘rod’ of water is likely to provide a better ground than a 2m rod of copper-clad steel.

I do, of course, agree with the need for the metal control box to be earthed.

Comments welcome.

[InterestedObserver]

With the submersible pump located 80m down a borehole and connected by PVC riser, from an electrical safety standpoint there is no way to come in contact with the metal pump casing. However, from an electrical fault protection standpoint there is merit to having the pump casing grounded (earthed) in case there is an insulation failure of one of the motor windings to ground. A solid ground fault should be cleared more rapidly by the instantaneous trip main circuit breaker than by a time delay thermal overload relay..

Edited November 3, 2010 by InterestedObserver

[electau]

There is a very good reason to earth the pump motor. Electrical safety.

The impedance of the line earth loop in ohms must be low enough with an earth fault to trip a protective device in this case an 16A/20A MCB in 0.4secs. This means that the earthing must be MEN and if you do not run a PE earth back to the main switch board you will have to MEN at the pump switch board. If you directly earth the pump to the general mass of earth as you propose you will require an RCD for fault protection, as an RCD is required to trip in less than 0.2/0.3 secs at 30mA.

Din rail mounting RCD/RCBOs are available and can be mounted within the switch board enclosure.

The line side to the pump switch board would not be RCD protected, protection would be on the load side of the pump switch board.

You indicate that the route length of the pump switch board to the pump motor is a minimum of 80M. this means that the loop impedance must not exceed 1.53 ohms for a type C 20A MCB. or 1.92 ohms with a 16A MCB.

If a 20A MCB and 2.5sqmm cable the max distance must not exceed 68 M and 85M if a 16A MCB is used.

Installing an RCD/RCBO meets the protection requirements as it trips in less than 0.4secs and at a lower fault current ie, 30mA.

( Source AS3000/2007.)

[Crossy]

I have a couple of issues with electau's post above.

Firstly, you should only ground your neutral at the incoming supply point, connections between neutral and ground at other points are not permitted (source BS7671 2008) so a local MEN would not be allowed. Indeed unless care is taken you could stop your RCD devices from tripping (or make them so they won't stay in).

If you don't want to export your MEN'd ground (another thing that BS7671 does not permit under certain circumstances) then the correct method would be to TT the pump supply with a local ground rod and RCD protection, I'd use a 100mA RCD to prevent nuisance tripping as in reality the danger of a direct or indirect contact shock when the pump is 30m down a well on a PVC pipe is negligible so a 30mA RCD would not be required.

Actually, my use of BS7671 above is really incorrect, under UK regulations consumers are not permitted to make ANY connection between N and E, all these links are taken care of by the supply authority and are sealed in the service head although BS7671 does indeed note that consumer fitted N-E links are not permitted.

What I'm really trying to say is, let's not be slaves to regulations that do not necessarily apply, neither the AS or BS regs have any bearing where we are (although they provide a good starting point), a pragmatic and practical approach is required in the absence of an actual standard to which we can work. TT is permitted here, so let's use it.

[Khonwan]

Thanks for your feedback InterestedObserver and thanks to Crossy’s pragmatism (as always). The British and Australian regulations indeed do not apply here. I’m sure that in UK or Australia, wiring installations must slavishly follow the codes but here in Thailand we can hopefully meet the objectives of those codes by applying rationality rather than slavishness.

I wonder how many farms in UK or Australia have their transformers located one mile from the farm-house – I suspect none. That is, I’m sure, why there should never be a need for the consumer to install a “MEN’d ground”. Thailand does not, it appears, prevent the consumer in my situation from installing such MEN’d grounds – on the contrary, they encourage it!

PEA installed my 3-ph transformer in full knowledge of the distance concerned – I installed everything else immediately after the transformer (ok, after the meter, which is mounted on the transformer pole). They had initially forgotten to tell me that I should have grounded my overhead neutral approximately every 200 meters. They told me this after my meter was struck by lightning (completely destroyed) around 9 times over the first couple of years. PEA replaced the meter for free each time, then eventually insisted I ground my neutrals as described, and also that I install a set of MOVs immediately after the meter.

So my grounding of the neutral at the borehole on a new overhead run of approximately 200 metres (spilt from my main breaker that is nearly 1500 metres after my transformer) is certainly in line with PEA’s advice to me. I should add that since grounding my neutrals every 200 metres (a very easy job) over a year ago, my meter has not been struck by lightning.

I have just purchased 100 metres of single-core earth cable to attach between the pump and my adjacent ground rod when the pump has to be raised to clean out the grit blocking it. I do not intend to pay another 6,000 baht for a 3-ph RCD in addition to the breaker and other protective devices already installed since I can conceive of no possible danger to life or limb from a pump 80 metres underground with a PVC riser.

[InterestedObserver]

From your meter experience, a set of MOVs might be a good idea in the submersible pump starter panel.

[Khonwan]

Good idea, thanks. I’ll try to locate something suitable – do you have a product model / supplier name?

[InterestedObserver]

Good idea, thanks. I'll try to locate something suitable – do you have a product model / supplier name?

I'm not familiar with the products available in Thailand. Did you install MOVs (surge protection) per recommendation of PEA? Crossy or electau will know what voltage and joule rating to use and what is available locally.

Edited November 8, 2010 by InterestedObserver

[Khonwan]

I purchased the MOVs(as specified by PEA – I’ll need to check with the local manager again as I can’t recall the spec; I think it cost me 2,000 baht for the 4-wire set) for connection to the overhead cables (240V) and PEA did me the favour by fitting them for free whilst doing something else (probably replacing the meter!). I could easily do the same at the borehole end – and probably will. I was interested, though, in the MOVs that could be fitted into the control box as you mentioned but I guess that the overhead MOVs would be more effective through size.

[InterestedObserver]

Look at the picture provided by Naam, Post #11, you can see the surge protectors (red blocks marked L, L, L, N) installed in his pump starter panel. The surge protection should be located as close to your submersible pump as possible.

[Khonwan]

Thanks. I think price may then be the deciding factor IF they are as efficient as the overhead MOVs. Placing inside the control box would be approximately 82m from the pump whereas on the overhead line would be approximately 83.5m – an insignificant difference.

[electau]

Electrical safety must be your first consideration, whether one uses the TT or MEN system.

If you use the TT system use an RCD.

Under AS3000 the MEN is at the main switchboard and more than one MEN is permitted with in an electrical installation eg farms with remote switchboards fed by aerial conductors.

Yes there is a difference between the AS and BS standards, and the AS are the easiest to apply in Thailand.

SPDs should be installed in the pump switch board protected by an 32 A DIN rail mtd MCB.

Earth conductor should be as short and direct as possible (no loops) min 6 sqmm Connect to main earthing conductor.

100kA per phase for an 8/20 micro sec impulse. Din rail mounting.

[Khonwan]

Electau, if electrical safety was not important to me I would not have ensured that every power point in my home is grounded (14 years ago) and then added an RCBO (1 year ago). But rather than quote overseas regulations (I only stress overseas since they have no legal force here) could you please tell me where you see the danger arising from a pump 80 metres underground with a PVC riser (no metal casing)? Show me the danger and I’ll both thank you and follow your advice. Money is not an issue but I detest slavishly following rules unless I can understand their rational.

“SPDs should be installed in the pump switch board” What does it matter whether they are in or immediately (as in 1.5m) outside? Please don’t tell me that the reason is to ensure closer proximity to the pump because I could then squeeze the MOVs/SPDs in between the switchboard and the well (separated by around 1.5 metres) Sounds to me like regulation quoting again – if so, I already have the full IEE Wiring Regulations 16th Edition (yes, I know it has been superseded by the 17th Edition) in hard print here in my house, in addition to The Electrician’s Guide to the 16th Edition by John Whitfield.

So, both you and Crossy say that if I ground to an adjacent earth rod I must install an RCD – do you both mean that not bothering to ground the pump is safer than grounding it only to an earth rod without RCD? Sounds crazy to me.

To tell you straight – I’m not looking for absolute perfection. I, and my children, happily live (without conflict) with a great many dangerous snakes on our farm adjacent to a hill forest/national park – I handle these regularly (without injury to them or me) and often find them in the pond (dam for you Aussies) with me as I swim. My point is that I’m trying to strike a reasonable balance in terms of safety – I’m not trying to eradicate risk.

My apologies if this comes across to strong. I know you mean well and I am grateful for your time.