Any sparky's on here, need advice. - Page 3

petespieces · 20th February 2014, 18:27

Quote:

Originally Posted by Perrin

Just out of interest, is it normal to have multiple earth rods on that type of system? Is it possible that there may be a potential difference between the two earths due to different chemistry where they are installed? How does that affect the earth rods themselves (i.e. corroding) and would that cause interference on electronics?
I'm no electrician by trade so I'm just curious.

OP do you then bond all metal such as plumbing to the earth?
Here we do, and it's bonded as i said to the neutral. Works well so long as the neutral is in tact. Neutral was stolen here one night about 10 years ago, and at the time (even with our power off) we still felt shocks occasionally till it was repaired!

Normal practice for multiple earth rods.

Plumbing is bonded at various points all through the house.

Perrin · 20th February 2014, 18:35

Here we use the TN-C-S for houses. My house is fed by a 300m 3phase 4 cable overhead feed which supplies all the houses up the road from me (we're last on the line, next door the other side is a different transformer).
Each pole has the neutral earthed via earth spike, and there is an earth spike at each meter box, and all but two have 3 phases.
But after the meter box the earth and neutral are separate.

i was wondering more about that TT arrangement, if 2 rods are installed within the house wiring, could it cause a potential difference?

I must say this is all very interesting learning how the different countries operate!

petespieces · 20th February 2014, 21:48

My plan is to install a second earth spike but the unit will also be connected to the existing earth system, I don't actually need to do that but just thought it would be a good idea in case the existing spike ever gets disconnected as was the case when we moved in, perhaps being overcautious but it was a shocking experience

Jumper75 · 25th February 2014, 02:15

2 phase appliance are rare, I've never seen one. In a 3 phase 400v system all the phases cancel out so no neutral required, but in your case some of the power returns via the neutral. My instinct is that as it's 400v power would return partly via the other phase and partly via neutral so only 1 2.5mm wire would be needed, but it depends on how the appliance is designed.

The easy way to know is put your clamp meter over the wires and see if the neutral carries the same current.

As far as RCDs go, you need a 4 pole 3 phase RCD, you also will want to test it with an RCD tester as a leak to a poor earth won't trip it. I believe france is on TT for domestic homes, in which case RCD protection is essential. Btw pressing the trip button on an RCD is not a valid test for a fault to earth.

Borg Warner · 25th February 2014, 14:36

Quote:

Originally Posted by Jumper75

2 phase appliance are rare, I've never seen one. In a 3 phase 400v system all the phases cancel out so no neutral required, but in your case some of the power returns via the neutral. My instinct is that as it's 400v power would return partly via the other phase and partly via neutral so only 1 2.5mm wire would be needed, but it depends on how the appliance is designed.

The easy way to know is put your clamp meter over the wires and see if the neutral carries the same current.

As far as RCDs go, you need a 4 pole 3 phase RCD, you also will want to test it with an RCD tester as a leak to a poor earth won't trip it. I believe france is on TT for domestic homes, in which case RCD protection is essential. Btw pressing the trip button on an RCD is not a valid test for a fault to earth.

2-ph systems are used quite a lot in rural areas in the UK. Saves a few bob on copper/aluminium cables. Useful for farms so they can have a larger capacity supply.

A 3-ph system requires a neutral return as it will be unbalanced; not having a neutral return will have very serious consequences. If you don't need a neutral why do you need a 4-pole RCD?

RCDs measure the current going in on the phase with what is coming out on the neutral, under normal circumstance these will be equal. However when an imbalance occurs e.g. current is flowing through you to earth they obviously operate.

Interesting to read about the French system, sounds a bit dodgy to me, especially as they are looking to build nuclear reactors over here. Think I'll buy a generator and a radioactive suit for me, wife and the wee dog.

Here's a picture of a 4-wire overhead LV system. The bottom wire is the neutral, top down is R-L1, Y-L2 and B-L3.

Jumper75 · 25th February 2014, 17:46

Ah, but that would be 460v split phase in UK rural areas, totally different, and yes common enough. Just not sure why an appliance manufacturer wants to use 2 phases at 120degrees out of a 3 phase supply.

The need for neutral, I was talking about 400v appliances not the whole installation which obviously needs neutral if you want any 230v appliances (maybe my post was not specific), 400v appliances are usually just 3P+E, but I've yet to see a whole installation where all 3 phases are in balance!

TT is more common worldwide than anything else, not the best in my opinion, I think it comes down to economics rather than safety.

As for RYB colours, wow that was a while ago now, and only in the UK. Even if the colours match the old french system (whatever that was) I'd still ignore it and check phase rotation, sparkys have a habit of using any colour they have left, often the same colour for all phases.

Quote:

Originally Posted by Borg Warner

2-ph systems are used quite a lot in rural areas in the UK. Saves a few bob on copper/aluminium cables. Useful for farms so they can have a larger capacity supply.

A 3-ph system requires a neutral return as it will be unbalanced; not having a neutral return will have very serious consequences. If you don't need a neutral why do you need a 4-pole RCD?

RCDs measure the current going in on the phase with what is coming out on the neutral, under normal circumstance these will be equal. However when an imbalance occurs e.g. current is flowing through you to earth they obviously operate.

Interesting to read about the French system, sounds a bit dodgy to me, especially as they are looking to build nuclear reactors over here. Think I'll buy a generator and a radioactive suit for me, wife and the wee dog.

Here's a picture of a 4-wire overhead LV system. The bottom wire is the neutral, top down is R-L1, Y-L2 and B-L3.

Perrin · 27th February 2014, 13:48

We still use Red White Blue or Red Yellow Blue down here, but you are right about the phase rotation. Our feed had red and blue swopped at the top of the power supplier's pole. Reason? Who knows! But if they do change this we will need to change our borehole pump (maybe you call it a well pump?) which is 3 phase.
Funny enough I was told that the TT system is supposed to be safer than Multiple Earth neutral or TN-C-S because fault currents won't be large so no possibility of a fire. Also, if you separate earth and neutral, then you won't have any elevated neutral voltages on your metalwork should the neutral become disconnected on the way back to the transformer.

I'm still wondering about lightning and its effect on the neutral considering it's bonded to earth. As I speak we have another storm rolling in (we get quite the show here!)

Perrin · 3rd May 2014, 07:51

Hello
I thought you guys might be interested in this article from our local newspaper last week after discussing earthing and possible problems.
http://randburgsun.co.za/225831/man-...electrocution/

I'm beginning to think the TT system is the better bet in the end!

Jumper75 · 8th May 2014, 01:37

Quote:

Originally Posted by Perrin

Hello
I thought you guys might be interested in this article from our local newspaper last week after discussing earthing and possible problems.
http://randburgsun.co.za/225831/man-...electrocution/

I'm beginning to think the TT system is the better bet in the end!

That house clearly has an additional fault inside the building, neutral is connected to earth somewhere.

That said, on a TNS system the live would then short via earth back to the transfromer and the fuses blow out, which would have indicated the fault straight away.

This presumablly was a TT system, and I'm still thinking that TNS is safer.

Gate Keeper · 8th May 2014, 03:20

Quote:

Originally Posted by Perrin

We still use Red White Blue or Red Yellow Blue down here, but you are right about the phase rotation. Our feed had red and blue swopped at the top of the power supplier's pole. Reason? Who knows! But if they do change this we will need to change our borehole pump (maybe you call it a well pump?) which is 3 phase.
Funny enough I was told that the TT system is supposed to be safer than Multiple Earth neutral or TN-C-S because fault currents won't be large so no possibility of a fire. Also, if you separate earth and neutral, then you won't have any elevated neutral voltages on your metalwork should the neutral become disconnected on the way back to the transformer.

I'm still wondering about lightning and its effect on the neutral considering it's bonded to earth. As I speak we have another storm rolling in (we get quite the show here!)

I am flying down to the cape on Saturday to the family farm for a month with my wife to do a check. We lost the farm and the houses to a bush fire in 2011 despite our efforts at the fire fighting. It took us 3 years to rebuild everything. I had to battle tooth and nail with the builders to get the earths fitted, as they claimed there is never any lightening and that they knew best ... duh! None of the house plugs have fuses in them, another mystery, as it is quite the thing to have them fitted in the UK. I installed surge protectors because of the power cuts. We have solar, but it is not possible for powering up everything. I am not having a go. It is an observation

3rd May 2014, 07:51	#28
Perrin Avid contributor Sold my Rover 75 Join Date: Oct 2013 Location: Johannesburg Posts: 101 Thanks: 33 Thanked 17 Times in 15 Posts	Unbelievable Hello I thought you guys might be interested in this article from our local newspaper last week after discussing earthing and possible problems. http://randburgsun.co.za/225831/man-...electrocution/ I'm beginning to think the TT system is the better bet in the end!

20th February 2014, 18:35	#22
Perrin Avid contributor Sold my Rover 75 Join Date: Oct 2013 Location: Johannesburg Posts: 101 Thanks: 33 Thanked 17 Times in 15 Posts	Here we use the TN-C-S for houses. My house is fed by a 300m 3phase 4 cable overhead feed which supplies all the houses up the road from me (we're last on the line, next door the other side is a different transformer). Each pole has the neutral earthed via earth spike, and there is an earth spike at each meter box, and all but two have 3 phases. But after the meter box the earth and neutral are separate. i was wondering more about that TT arrangement, if 2 rods are installed within the house wiring, could it cause a potential difference? I must say this is all very interesting learning how the different countries operate!

20th February 2014, 21:48	#23
petespieces Gets stuck in Rover 75 Saloon 1.8 auto Join Date: Mar 2012 Location: Le Theil de Bretagne (France) Posts: 661 Thanks: 36 Thanked 37 Times in 29 Posts	My plan is to install a second earth spike but the unit will also be connected to the existing earth system, I don't actually need to do that but just thought it would be a good idea in case the existing spike ever gets disconnected as was the case when we moved in, perhaps being overcautious but it was a shocking experience

25th February 2014, 02:15	#24
Jumper75 Loves to post Rover 75 Connoisseur CDT Tourer Join Date: Aug 2010 Location: Cardigan Posts: 358 Thanks: 6 Thanked 49 Times in 44 Posts	2 phase appliance are rare, I've never seen one. In a 3 phase 400v system all the phases cancel out so no neutral required, but in your case some of the power returns via the neutral. My instinct is that as it's 400v power would return partly via the other phase and partly via neutral so only 1 2.5mm wire would be needed, but it depends on how the appliance is designed. The easy way to know is put your clamp meter over the wires and see if the neutral carries the same current. As far as RCDs go, you need a 4 pole 3 phase RCD, you also will want to test it with an RCD tester as a leak to a poor earth won't trip it. I believe france is on TT for domestic homes, in which case RCD protection is essential. Btw pressing the trip button on an RCD is not a valid test for a fault to earth.

27th February 2014, 13:48	#27
Perrin Avid contributor Sold my Rover 75 Join Date: Oct 2013 Location: Johannesburg Posts: 101 Thanks: 33 Thanked 17 Times in 15 Posts	We still use Red White Blue or Red Yellow Blue down here, but you are right about the phase rotation. Our feed had red and blue swopped at the top of the power supplier's pole. Reason? Who knows! But if they do change this we will need to change our borehole pump (maybe you call it a well pump?) which is 3 phase. Funny enough I was told that the TT system is supposed to be safer than Multiple Earth neutral or TN-C-S because fault currents won't be large so no possibility of a fire. Also, if you separate earth and neutral, then you won't have any elevated neutral voltages on your metalwork should the neutral become disconnected on the way back to the transformer. I'm still wondering about lightning and its effect on the neutral considering it's bonded to earth. As I speak we have another storm rolling in (we get quite the show here!)