Earth spike

[Kurt]

I am having a 32A outside circuit fitted from my consumer unit to power a hottub. The cable is 6mm armoured, and about 40M in length.

1. Is there any IEE Regs requirement to use an earth spike anywhere in this circuit. If not, why do you think the hottub supplier may have recommended that I fit one.

2. Should my sparky be fitting 2 core or three core cable (it is a standard single phase 230v circuit)

Thanks.

 

[ban-all-sheds]

I am having a 32A outside circuit fitted from my consumer unit to power a hottub. The cable is 6mm armoured, and about 40M in length.

What's the actual load of the hot-tub? 6mm² is close to the limit for VD at 32A over that distance, 10mm² might be better, but then again if you won't actually be drawing 32A...
But then again the other way - what if you decide that you'd like extra stuff out there at some point, like floodlights, or heaters? Given the marginal cost difference maybe you should consider 10mm² anyway.

1. Is there any IEE Regs requirement to use an earth spike anywhere in this circuit. If not, why do you think the hottub supplier may have recommended that I fit one.

Do you know what type of supply you have (TT/TN-S/TN-C-S)?

2. Should my sparky be fitting 2 core or three core cable (it is a standard single phase 230v circuit)

If he's a proper sparky he should work that out - I don't have the figures to hand right now, but there is potentially an issue with using the armour as the cpc if its resistance is too high to allow you to get the disconnection time you need.

 

[Kurt]

Thanks for your reply.

What's the actual load of the hot-tub?

I don't know. The supplier has not shown me any electrical specifications, except to tell me that I need a 32A/32mA RCD circuit with an IP56 isolator.

6mm² is close to the limit for VD at 32A over that distance, 10mm² might be better, but then again if you won't actually be drawing 32A...
But then again the other way - what if you decide that you'd like extra stuff out there at some point, like floodlights, or heaters? Given the marginal cost difference maybe you should consider 10mm² anyway.

You make a good point, and this is what I have found looking at tlc-direct's web based calculator. This distance is on the edge of 10mm cable.
I am a little concerned as the sparky was recommending 4mm for the job and I brought him round to the idea that 6mm might be better. Should I trust him to do the job?

Do you know what type of supply you have (TT/TN-S/TN-C-S)?

Unfortunately I don't know enough about electrics to answer that. Although I can say that the property is *not* fed by an overhead cable, and was built 18 months ago. Is it possible to tell from that?


Thanks.

 

[ban-all-sheds]

You make a good point, and this is what I have found looking at tlc-direct's web based calculator. This distance is on the edge of 10mm cable.
I am a little concerned as the sparky was recommending 4mm for the job and I brought him round to the idea that 6mm might be better. Should I trust him to do the job?

Maybe he has experience of these spas, and knows that the constant current is a lot lower than 30A, but there's a big start-up surge (let's hope so, or it's going to be an expensive thing to run...), in which case 4mm² may be fine, and 6mm² will give you capacity for the future. Do the specs not say what the rating of the breaker or fuse on the circuit should be? a 32A/30mA RCD just means that it can switch 32A off, it doesn't actually provide overload protection, so there will need to be an MCB or fuse as well....

Do you know what type of supply you have (TT/TN-S/TN-C-S)?

Unfortunately I don't know enough about electrics to answer that. Although I can say that the property is *not* fed by an overhead cable, and was built 18 months ago. Is it possible to tell from that?

Is there a warning label where the cable from your main earth terminal joins the incoming service cable, talking about PME?

 

[Lectrician]

We do many hot tubs, 32amp is common place, and the loading is 16 to 20 ish amps for the thermostaticly controlled heater, and the pumps/lights and stereo use the rest. (you can flick a switch inside most tubs to switch the heater OFF when the pumps etc are running to alleviate loading)

 

[ban-all-sheds]

In that case 4mm² is pushing it. It is within limits, but only just.

 

[Kurt]

Is there a warning label where the cable from your main earth terminal joins the incoming service cable, talking about PME?

I can't tell. The CU is mounted on a plasterboard wall and all other wiring is concealed behind the plasterboard. I presume that if there was supposed to be a notice it should be obvious. The only notices that I can see are on the CU. One mentions the RCD and talks about testing it with the button, the other is a signed label with the date of installation of the CU.

I need some way of finding out whether or not I need to install an earth spike. Can anyone offer me any suggestions on how I may determine this?

Many thanks.

 

[Kurt]

I have dug out a domestic electrical installation certificate for the property and it says the 'System Type' is TN-C-S. It also says that the 'Means of Earthing' is 'Supplier's Facility'.

Can anyone tell from this if I need an earth spike outside?

Which system's would need one - and why?

Thanks.

 

[plugwash]

ahh TN-C-S aka PME aka f*cking cheap recs

with a TN-C-S it is best to connect any outside wiring to its own rod which should be kept completely seperate from the rest of the house wiring due to the possibility of a break in the suppliers neutral core

installing rods however is NOT a diy job due to the testing needed and the risk from connecting to the house earth is pretty small

also will there be any water piping to the hot tub and will this be metal or plastic (plastic is better from an electrical point of view)

 

[Kurt]

ahh TN-C-S aka PME aka f*cking cheap recs

What does "recs" mean? I understand the rest.

with a TN-C-S it is best to connect any outside wiring to its own rod which should be kept completely seperate from the rest of the house wiring due to the possibility of a break in the suppliers neutral core

When you say "best", does that mean it is a recommendation, or is it part of the IEE regs?

and the risk from connecting to the house earth is pretty small

What does this mean?

also will there be any water piping to the hot tub and will this be metal or plastic (plastic is better from an electrical point of view)

No, it gets filled by a hose pipe, the electricity is used to feed a heater and a pump. Does this affect whether or not I need an earth rod?

Thanks a lot.

 

[masona]

Kurt, I'm not a electrician but there's some information regarding earth rod from FWL_Engineer.

See here.

 

[securespark]

Regional Electricity Company