Farm electrics

[RF Lighting]

My first reaction is FFS & is the installation adequate for such a load to be added?

Then I think of the plant I'm accustomed to and massive supplies to chillers and associated plant on roofs and ground level compounds is common and never RCD protected. If livestock cannot gain access to the new plant I see no difference. However I'd have expected to see some sort of control panel taking a single supply and not multiple supplies to complicate isolation.

Personally I's still liked to see RCD.

The problem is that because it is a TT supply, should one of the chiller compressors for example go short circuit to earth, the Zs is too high to cause the circuit breaker to open, so the earth for entire installation will rise in potential to dangerous levels and sit there until someone receives a shock.

 

[SUNRAY]

That's quite good for farm.

Some places would have demolished the barn and left that lot tied to a fence post with a fertiliser bag over it.

I have seen exactly that... 3 times

 

[SUNRAY]

The problem is that because it is a TT supply, should one of the chiller compressors for example go short circuit to earth, the Zs is too high to cause the circuit breaker to open, so the earth for entire installation will rise in potential to dangerous levels and sit there until someone receives a shock.

Quite so and why I'd have prefered to see RCD's

 

[RF Lighting]

I’d have said they are an absolute mandatory requirement and anyone not fitting them is criminally negligible, rather than it is preferable to use them.

 

[SimonH2]

And the obvious question is ... what did you do about it (the "dodgy" chiller install) ?

 

[SUNRAY]

I’d have said they are an absolute mandatory requirement and anyone not fitting them is criminally negligible, rather than it is preferable to use them.

Ah I managed to delete part of my post.
Based on my experiences I'd made assumptions such as: They'd put down new TT earth for the chiller and it's otherwise electrically isolated from the parlour including plastic piping etc between the two.

I've also assumed the chiller is a separate location, ie not in the parlour building.

 

[Adam_151]

Whilst working there today, we noticed that the farm have had a new bulk storage tank and associated chillers installed by specialist dairy company. They have taken two 32A triple pole type C supplies and one 16A single pole type C supply from the TT’d parlour installation to supply their equipment without any RCD protection at all.

Does the installation not have any rcd protection on the incomming supply? I'd nomally expect a 100mA/300mA time delay device on the smaller installations, while larger ones would have an MCCB fitted with a shunt trip fired by an adustible earth fault relay (granted it might be set for a longer delay than 0.2s but that would not be as bad as no fault protection)

 

[SUNRAY]

Does the installation not have any rcd protection on the incomming supply? I'd nomally expect a 100mA/300mA time delay device on the smaller installations, while larger ones would have an MCCB fitted with a shunt trip fired by an adustible earth fault relay (granted it might be set for a longer delay than 0.2s but that would not be as bad as no fault protection)

I didn't even consider this was NOT in place, My consideration was based solely on the usual 30mA part of the system.

 

[RF Lighting]

Does the installation not have any rcd protection on the incomming supply? I'd nomally expect a 100mA/300mA time delay device on the smaller installations, while larger ones would have an MCCB fitted with a shunt trip fired by an adustible earth fault relay (granted it might be set for a longer delay than 0.2s but that would not be as bad as no fault protection)

No. The DNO supply to the site is a 100A TP&N TN-C-S supply. The feed to the parlour is an SWA cable earthed at the supply end with the TN-C-S earth which is not connected to the parlour installation.

 

[Adam_151]

No. The DNO supply to the site is a 100A TP&N TN-C-S supply. The feed to the parlour is an SWA cable earthed at the supply end with the TN-C-S earth which is not connected to the parlour installation.

So at the parlour end, standard 3ph board with the SWA taken through a stuffing gland or similar and 30mA RCBOS on all outgoing circuits?

 

[SimonH2]

Based on my experiences I'd made assumptions such as: They'd put down new TT earth for the chiller and it's otherwise electrically isolated from the parlour including plastic piping etc between the two.

Unlikely.
The plumbing between chiller & bulk tank is normally high pressure refrigerant pipework - I believe CO2 in copper pipe is common.
So the tank, in the dairy and definitely within reach of metalwork that's part of your original earthing scheme, will be electrically connected to the new chiller via the pipework.

 

[bernardgreen]

As SimonH2 has mentioned, there are many opportunities for sneak paths between a TT CPC Earthed by a Ground Electrode(s) and another separate CPC Earthed by connection an incoming supply Neutral or supply Earth.

 

[SUNRAY]

Unlikely.
The plumbing between chiller & bulk tank is normally high pressure refrigerant pipework - I believe CO2 in copper pipe is common.
So the tank, in the dairy and definitely within reach of metalwork that's part of your original earthing scheme, will be electrically connected to the new chiller via the pipework.

As SimonH2 has mentioned, there are many opportunities for sneak paths between a TT CPC Earthed by a Ground Electrode(s) and another separate CPC Earthed by connection an incoming supply Neutral or supply Earth.

Again more assumptions based on limited experience on my part. Yes the refrigerant pipes are most likely to be brazed copper

When I were a kid I had several summer holidays with my grandparents and visits to farms, with an Uncle who made his living doing general agricultural maintenance, was a common thing. I clearly remember the sad rusting and very mucky parlours with the rotting white painted steel pipes & ribbed red rubber hoses but that was 55 years ago.
More recently I've worked in 3 control panels on dairy farms and each had the storage remote from the parlour and care had been taken to keep them electrically isolated with all control between the parlour and panel being SELV generated at the parlour [one was an ethernet connected Trend outstation].

I'd therefore assumed that as this is under 10 years old it's built to the same methods as my recent experience and the bulk tank is not in the parlour. I'm accustomed to the milk pipes being a combination of clear solid and flexible plastic replacing what used to be mild steel [then stainless steel] and rubber.

I don't have enough experience of dairy farms to know how typical the 3 I've worked in are of current trends.

Likewise the heating/ventilation systems I'm accustomed to working on are bespoke to each situation and there is no such thing as a standard system, it would be silly to think dairy farms would be any different but so far I have been making that mistake if it is one

 

[SimonH2]

In my experience, but that's not exactly extensive in the grand scheme of things. And some of it may be dated, so there may be more plastics used these days ...

Yes, the dairy with bulk tank and washing facilities is separate from the parlour - but is often linked to it, being totally separate is not that common.

Pipework is typically galvanised steel for the vacuum pipes, and stainless steel or glass for the milk pipes. Rubber (or rubber like plastics) are generally only used for coupling together the stainless or glass pipes, and where flexibility is required. Glass is preferred for the milk pipes as it has a smoother surface and is easier to keep clean (scale, a.k.a. milkstone tends to build up on stainless pipes unless a quite aggressive cleaner is used).
Galv vacuum pipework is typically used to support the rest fo the pipework, having that nice characteristic of being quite stiff.

I'd be sceptical of accepting insulating pipework as satisfactory isolation between parlour and dairy. I'm fairly certain that milk is conductive, and even if you ignore that, then you still have the issue of supporting a run of pipework over enough distance to not create a hazard to someone able to touch both sides of the insulating section. Oh yes, don't forget condensation (especially on the inside of the vacuum pipework, and a good coating of "dirt" that will collect on top of all the pipes in between periodic deep cleans that will also be conductive when damp.

I could understand some modern systems using SELV, that certainly wasn't the case back when I last had in depth knowledge - it must be 40 years since I help someone build their new new "modern" farm unit and parlour. TN-C-S, minimal bonding to structural steelwork, all mains powered equipment - and given what I know now, something to be concerned about.

The main positive feature is likely to be the ubiquitous use for green wellies which I suspect are reasonably good insulators.

 

[SUNRAY]

In my experience, but that's not exactly extensive in the grand scheme of things. And some of it may be dated, so there may be more plastics used these days ...

Yes, the dairy with bulk tank and washing facilities is separate from the parlour - but is often linked to it, being totally separate is not that common.

Pipework is typically galvanised steel for the vacuum pipes, and stainless steel or glass for the milk pipes. Rubber (or rubber like plastics) are generally only used for coupling together the stainless or glass pipes, and where flexibility is required. Glass is preferred for the milk pipes as it has a smoother surface and is easier to keep clean (scale, a.k.a. milkstone tends to build up on stainless pipes unless a quite aggressive cleaner is used).
Galv vacuum pipework is typically used to support the rest fo the pipework, having that nice characteristic of being quite stiff.

I'd be sceptical of accepting insulating pipework as satisfactory isolation between parlour and dairy. I'm fairly certain that milk is conductive, and even if you ignore that, then you still have the issue of supporting a run of pipework over enough distance to not create a hazard to someone able to touch both sides of the insulating section. Oh yes, don't forget condensation (especially on the inside of the vacuum pipework, and a good coating of "dirt" that will collect on top of all the pipes in between periodic deep cleans that will also be conductive when damp.

I could understand some modern systems using SELV, that certainly wasn't the case back when I last had in depth knowledge - it must be 40 years since I help someone build their new new "modern" farm unit and parlour. TN-C-S, minimal bonding to structural steelwork, all mains powered equipment - and given what I know now, something to be concerned about.

The main positive feature is likely to be the ubiquitous use for green wellies which I suspect are reasonably good insulators.

That is fairly well compatible with my experience except all the pipes between the 2 are insulating [or so I believe], I'd assumed plastic but glass does of course make more sense.

All 3 control panels I've dealt with had a very strict barrier between the 2 sets of wiring to the point that the parlours SELV appeared in a plastic enclosure, the store section is s/steel and the barrier is the junction between them.