Hot tub wiring

[Igor Taranenko]

Hi All,

I have a job to install 32A supply for hot tub. 6mm armoured cable around 40M. Can't be collected to existing CU as no spares there. But there is a small CU right next to the meter (pictures provided) which supply power to car charger. Meter tails to this CU is 16mm which is OK to supply both car charger and hot tub.
Question is: can I fit RCBO for the hot tub to this consumer unit connecting it to a supply side of existing RCBO for car charger?
Or maybe there is another way?
Thanks

 

[pc1966]

The main issues for adding another RCBO are:

• It would need to be a DP RCBO as there is no other DP isolation before that.
• Because of that you would need the DNO to pull the fuse to work on it.
• You would have to check the existing RCBO, etc, can take both the tails and sufficient conductor size to feed the hot-tub RCBO as well (as no bus-bars present).
• You might need to take the SWA to the top as it looks limited space/bend radius below.

[automerge]1591434834[/automerge]
Thinking again, as you would have to pull the DNO fuse anyway, it might be worth looking to replace the existing arrangement with one that has a DP isolation switch and then the two RCBO you need. Certainly a lot less trouble in the future (e.g. RCBO replacement), and more obvious means of isolation, along with an approved bus-bar for feeding them, etc.

Wylex & Crabtree single module RCBOs have switched neutrals so would preserve that aspect.
[automerge]1591435244[/automerge]
This sort of thing:

Wylex NM206/63 NM Series Amendment 3 All Metal 2 Way Consumer Unit With Switch Disconnector Isolator 63A, NM206/63

NM206/63 The Wylex NM206/63 all metal consumer unit is fully compliant with Amendment 3 to BS 7671:2008. Supplied with 63A switch isolator. The consumer unit can be populated with up to 2 RCBOs. The NM206/63 allows for total isolation of circuits and is the best choice to achieve a 17th edition...

www.discount-electrical.co.uk

Wylex NHXS1B40 1 Module SP+SN Miniature Type B RCBO 40A 6kA 30mA, NHXS1B40

NHXS1B40 Wylex NHXS1B40 40A 6kA 30mA SP+SN reduced height Type B RCBO for domestic and similar installations are compatible with NM Amendment3 all-metal consumer units which are compliant with the new 18th Edition wiring regulations. <br><br> The RCBO combines the overcurrent functions...

www.discount-electrical.co.uk

 

[Igor Taranenko]

The main issues for adding another RCBO are:

• It would need to be a DP RCBO as there is no other DP isolation before that.
• Because of that you would need the DNO to pull the fuse to work on it.
• You would have to check the existing RCBO, etc, can take both the tails and sufficient conductor size to feed the hot-tub RCBO as well (as no bus-bars present).
• You might need to take the SWA to the top as it looks limited space/bend radius below.

[automerge]1591434834[/automerge]
Thinking again, as you would have to pull the DNO fuse anyway, it might be worth looking to replace the existing arrangement with one that has a DP isolation switch and then the two RCBO you need. Certainly a lot less trouble in the future (e.g. RCBO replacement), and more obvious means of isolation, along with an approved bus-bar for feeding them, etc.

Wylex & Crabtree single module RCBOs have switched neutrals so would preserve that aspect.
[automerge]1591435244[/automerge]
This sort of thing:

Wylex NM206/63 NM Series Amendment 3 All Metal 2 Way Consumer Unit With Switch Disconnector Isolator 63A, NM206/63

NM206/63 The Wylex NM206/63 all metal consumer unit is fully compliant with Amendment 3 to BS 7671:2008. Supplied with 63A switch isolator. The consumer unit can be populated with up to 2 RCBOs. The NM206/63 allows for total isolation of circuits and is the best choice to achieve a 17th edition...

www.discount-electrical.co.uk

Wylex NHXS1B40 1 Module SP+SN Miniature Type B RCBO 40A 6kA 30mA, NHXS1B40

NHXS1B40 Wylex NHXS1B40 40A 6kA 30mA SP+SN reduced height Type B RCBO for domestic and similar installations are compatible with NM Amendment3 all-metal consumer units which are compliant with the new 18th Edition wiring regulations. <br><br> The RCBO combines the overcurrent functions...

www.discount-electrical.co.uk

Thanks for sharing your thoughts. I have had in mind rearranging in my self by fitting DP main switch and 2 RCBOs. Didn't think there are DP switched ones for single modules. Also for me rearranging would be practical and satisfying requirements. As for fitting swa, I'm thinking to take 6mm t&e inside this meter box to a wiska box or similar right next to meter enclosure where I can gland swa.

 

[Igor Taranenko]

The main issues for adding another RCBO are:

• It would need to be a DP RCBO as there is no other DP isolation before that.
• Because of that you would need the DNO to pull the fuse to work on it.
• You would have to check the existing RCBO, etc, can take both the tails and sufficient conductor size to feed the hot-tub RCBO as well (as no bus-bars present).
• You might need to take the SWA to the top as it looks limited space/bend radius below.

[automerge]1591434834[/automerge]
Thinking again, as you would have to pull the DNO fuse anyway, it might be worth looking to replace the existing arrangement with one that has a DP isolation switch and then the two RCBO you need. Certainly a lot less trouble in the future (e.g. RCBO replacement), and more obvious means of isolation, along with an approved bus-bar for feeding them, etc.

Wylex & Crabtree single module RCBOs have switched neutrals so would preserve that aspect.
[automerge]1591435244[/automerge]
This sort of thing:

Wylex NM206/63 NM Series Amendment 3 All Metal 2 Way Consumer Unit With Switch Disconnector Isolator 63A, NM206/63

NM206/63 The Wylex NM206/63 all metal consumer unit is fully compliant with Amendment 3 to BS 7671:2008. Supplied with 63A switch isolator. The consumer unit can be populated with up to 2 RCBOs. The NM206/63 allows for total isolation of circuits and is the best choice to achieve a 17th edition...

www.discount-electrical.co.uk

Wylex NHXS1B40 1 Module SP+SN Miniature Type B RCBO 40A 6kA 30mA, NHXS1B40

NHXS1B40 Wylex NHXS1B40 40A 6kA 30mA SP+SN reduced height Type B RCBO for domestic and similar installations are compatible with NM Amendment3 all-metal consumer units which are compliant with the new 18th Edition wiring regulations. <br><br> The RCBO combines the overcurrent functions...

www.discount-electrical.co.uk

NHXS 40A Single Pole 1 Module B Curve 6kA 30mA RCBO

Built in switched neutral

www.cef.co.uk

Am I right thinking that this is the same just from CEF. DP switched?

 

[pc1966]

Am I right thinking that this is the same just from CEF. DP switched?

Yes, same range.
[automerge]1591447880[/automerge]

As for fitting swa, I'm thinking to take 6mm t&e inside this meter box to a wiska box or similar right next to meter enclosure where I can gland swa.

That would allow tighter bends, etc, so might be your best bet.

If you are fitting T&E to the metal CU you can get glands for that for a professional finish:

Sprint Cable Glands

For 6mm you need a 25mm hole though, not sure what most garage CU come with but probably 20 so out with the step-drill, etc!

 

[Igor Taranenko]

Yes, same range.
[automerge]1591447880[/automerge]

That would allow tighter bends, etc, so might be your best bet.

If you are fitting T&E to the metal CU you can get glands for that for a professional finish:

Sprint Cable Glands

For 6mm you need a 25mm hole though, not sure what most garage CU come with but probably 20 so out with the step-drill, etc!

Description for RCBO is rather confusing, it's says 1 pole but in specifications under "number of poles" it's says "single pole & neutral.
Will certainly get m25 gland to house 6mm t&e into small CU.
Another interesting thing I'VE found that existing car charger rcbo seems to be type C? I've checked reg book and it says that charger must be protected by RCD of at least type A

 

[radiohead]

Description for RCBO is rather confusing, it's says 1 pole but in specifications under "number of poles" it's says "single pole & neutral.
Will certainly get m25 gland to house 6mm t&e into small CU.
Another interesting thing I'VE found that existing car charger rcbo seems to be type C? I've checked reg book and it says that charger must be protected by RCD of at least type A

Type C refers to the overcurrent part of the RCBO,not the RCD.

 

[pc1966]

Description for RCBO is rather confusing, it's says 1 pole but in specifications under "number of poles" it's says "single pole & neutral.
Will certainly get m25 gland to house 6mm t&e into small CU.

Strictly speaking it is single pole and switched neutral because it is not sensing over-current on the neutral, just the line. A true DP breaker will trip on over current on any pole. However, it is isolating both if it trips, where as most single pole RCBO do not (but they have to have the neutral pass through them to sense the current imbalance).

Another interesting thing I'VE found that existing car charger rcbo seems to be type C? I've checked reg book and it says that charger must be protected by RCD of at least type A

OK, you would be looking for this:

NHXS 40A Single Pole 1 Module C Curve 6kA 30mA RCBO

Built in switched neutral

www.cef.co.uk

For some dumb reason they decided to give RCDs codes like this:

• AC = works on AC faults only
• A = AC and pulsing DC faults
• B = also DC faults
• F = AC and high frequency faults (e.g. inverters)

But for the MCB they use the B/C/D designator for how sensitive the "instantaneous" magnetic trip is:

• B = 3-5 * In
• C = 5-10 * In
• D = 10-20 * In

So now if you see 'type B' for an RCBO you can not be sure if it is DC-sensitive or simply the B-curve and no RCD destination offered!
[automerge]1591451017[/automerge]
Ah, I see radiohead beat me to it!

More info on RCDs here:

http://www.doepke.co.uk/download/Techpub-16

 

[Igor Taranenko]

Strictly speaking it is single pole and switched neutral because it is not sensing over-current on the neutral, just the line. A true DP breaker will trip on over current on any pole. However, it is isolating both if it trips, where as most single pole RCBO do not (but they have to have the neutral pass through them to sense the current imbalance).


OK, you would be looking for this:

NHXS 40A Single Pole 1 Module C Curve 6kA 30mA RCBO

Built in switched neutral

www.cef.co.uk

For some dumb reason they decided to give RCDs codes like this:

• AC = works on AC faults only
• A = AC and pulsing DC faults
• B = also DC faults
• F = AC and high frequency faults (e.g. inverters)

But for the MCB they use the B/C/D designator for how sensitive the "instantaneous" magnetic trip is:

• B = 3-5 * In
• C = 5-10 * In
• D = 10-20 * In

So now if you see 'type B' for an RCBO you can not be sure if it is DC-sensitive or simply the B-curve and no RCD destination offered!
[automerge]1591451017[/automerge]
Ah, I see radiohead beat me to it!

More info on RCDs here:

http://www.doepke.co.uk/download/Techpub-16

Something I've definitely learnt today) many thanks for clearing out confusions in my head!

 

[telectrix]

Yes, same range.
[automerge]1591447880[/automerge]

That would allow tighter bends, etc, so might be your best bet.

If you are fitting T&E to the metal CU you can get glands for that for a professional finish:

Sprint Cable Glands

For 6mm you need a 25mm hole though, not sure what most garage CU come with but probably 20 so out with the step-drill, etc!

6mm up to 5 core will fit into a 20mm gland. either a 20S for up to 3 core (3 core may be borderline on a 20S) or a 20L for 4 and 5 core

 

[pc1966]

6mm up to 5 core will fit into a 20mm gland. either a 20S for up to 3 core (3 core may be borderline on a 20S) or a 20L for 4 and 5 core

Yes, for SWA, but I was meaning for the plastic T&E glands such as this one:

25mm Entry Gland for 6mm Flat T & E - IP68 LSF | Wiska (WKP25F6 / 10106240)