Hager MCB Replacement

[schapmande13]

Hi,

I have a Hager consumer unit and need to replace a Hager 32A MCB (link below) with a 45A MCB. This is required by my Mira (Shower Manufacturer) in order for them to come out and repair a faulty shower. The Hager MCB's only seem to be available in 40 or 50A.

http://www.hager.co.uk/product-cata...-6ka-type-b/mtn132/42123.htm?utm_source=print

Does anyone know if other manufactures 45A MCB's will fit, or whether there would be any issue with fitting a 50A Hager MCB. The shower manual is fairly specific that a 45A rated MCB is required.

http://www.hager.co.uk/product-cata...-6ka-type-b/mtn132/42123.htm?utm_source=print

 

[JohnW2]

Does anyone know if other manufactures 45A MCB's will fit ....

In theorety you should not do that, even if it will 'fit'

... or whether there would be any issue with fitting a 50A Hager MCB. The shower manual is fairly specific that a 45A rated MCB is required.

Electrically speaking (and in terms of the Wiring Regulations), there would be no issue provided that the cable, as installed, was meaty enough to be adequately protected by a 50A MCB (that would have to be checked). However, Mira can make up any rules they want!

Kind Regards, John

 

[Iggifer]

Assuming you have a 'split board' with two RCDs, your choices are 40 or 50A

If you only have one RCD and some circuits just protected by MCBs, Hager make a 45A RCBO

ADN145 is the part number

 

[schapmande13]

Here's a picture of the consumer unit, its the grey MCB on the left that needs replacing. I think this is the one that is only available in 40 or 50A?

The cable is 10mm2, with this in mind will a 50A MCB be ok?

 

[Iggifer]

Correct. However it could be moved over to the right hand side of the board (where there is no RCD and then the RCBO would do the job of the RCD and MCB. About £22. £20 more than an MCB but it depends how finicity Mira are being.

What size cable is it? If it's 6mm² you can't use a 50A anyway so that's out. A 45A is fine on 6mm² dependant on installation method of the cable

 

[JohnW2]

Assuming you have a 'split board' with two RCDs, your choices are 40 or 50A

... although, as I wrote earlier, a 50A one would only be an option if the cable (as installed) were up to it.

Kind Regards, John

 

[Iggifer]

... although, as I wrote earlier, a 50A one would only be an option if the cable (as installed) were up to it.

Kind Regards, John

Yup. Dealt with that in my post that I must have posted as you were typing

 

[schapmande13]

its 10mm2 cable so should be fine?

 

[Iggifer]

Yeah that should be fine on a 50A, if it's definitely 10mm², begs the question why it was put on a 32A in the first place!

 

[EFLImpudence]

You could use a 50A with 6mm² as long as the shower is rated less than the cable. It can't cause an overload.

 

[JohnW2]

You could use a 50A with 6mm² as long as the shower is rated less than the cable. It can't cause an overload.

You could, theoretically, but it stands a significant risk of causing hassle/argument if, say, there was a subsequent EICR, since I am fairly sure that many do not think beyond "Iz≥In≥Ib".

Furthermore, invoking the 'exception' to which you refer still requires that adequate fault protection be present, and that has the potential to be a problem with 6mm² cable, at least with a TN-S installation. The 'maximum Zs" for a B50 is 0.87Ω, and 6mm² cable has an R1+R2 of 12.65 mΩ/metre. That means that in the 'worse case of TN-S (Ze = 0.8Ω), one could not have more than about 5.5 metres of 6mm² cable - and I don't personally think that one should (in a TN installation) rely on an RCD as the primary provider of fault protection.

Kind Regards, John

 

[EFLImpudence]

Well, ok, but saying you can't do it is incorrect.
You mean they're not going to test it properly?

I really do not think doing things compliantly should be rejected because the next person may not know what they are doing.

If 5.5m is all it works out at on 6mm², then 10mm² will only allow 9m.
(I make 6mm²/2.5² 10.4mΩ/m. and 10mm²/4mm² 6.43mΩ/m)

It's very rarely the worst case 0.8Ω.



Is OP sure it is 10 square mm?

As said, why, then, is there a 32A MCB?

 

[JohnW2]

I really do not think doing things compliantly should be rejected because the next person may not know what they are doing.

I also think that it should not have to be rejected. However, in the real world, the great majority of householders know nothing of these technicalities, so probably wouldn't even think that there is any reason to question someone who (maybe years later) 'fails' the circuit and, even if they did question, would probably be convinced when that someone (who "does not know what they are doing") showed them the "Iz≥In≥Ib" regulation and demonstrated how their circuit fails to satisfy it. Even for you and me, the hassle of having to argue, if that happened, might make us decide against that course.

I make 6mm²/2.5² 10.4mΩ/m. ...

I was just using the Table 4D5 figures - do yours perhaps relate to some different temperature?

It's very rarely the worst case 0.8Ω.

Agreed, but that doesn't alter my point.

If you're one of those people who believe that it is acceptable (in TN installations) to rely upon an RCD as the only fault protection, then one could logically extend to argument to saying that one didn't need an OPD at all for a shower, immersion or whatever circuit!

Is OP sure it is 10 square mm? As said, why, then, is there a 32A MCB?

Those are very valid questions. ... or, the other way around, if a 32A MCB was adequate (maybe even 'specified' by manufacturer) (say for a 7.5kW shower), then why 10mm² cable (maybe for 'future proofing', I suppose).

Kind Regards, John

 

[EFLImpudence]

I was just using the Table 4D5 figures - do yours perhaps relate to some different temperature?

Ah. they are for 70°. Do you need that for fault current?
Anyway, I just know 10mm² is 1.83mΩ/m at 20° and calculate the other CSAs.

If you're one of those people who believe that it is acceptable (in TN installations) to rely upon an RCD as the only fault protection,

Not really but I now have to - until I play with my green and yellow one day.

then one could logically extend to argument to saying that one didn't need an OPD at all for a shower, immersion or whatever circuit!

mmmm. short circuit?

 

[JohnW2]

Ah. they are for 70°. Do you need that for fault current?

Dunno - but it would be a bit odd if one were allowed to confirm that the Zs was ('just') OK for ADS at a lower temperature but then a fault occurred when the cable happened to be at 70 (or whatever).

Not really but I now have to - until I play with my green and yellow one day.

If there is currently a paucity of G/Y, then presumably nothing in providing ADS in the event of faults between L and exposed-c-ps (other than your kitchen circuit)?

mmmm. short circuit?

You mean an L-N short? If so, are you postulating a requirement to protect against that even when it is permissible for over-current protection to be omitted?

Kind Regards, John