Shower Help Needed Installing new Triton 8.5kw on Protected 32amp Circuit


Postby paultoolbox » Tue Sep 05, 2017 3:50 pm

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hello i`m replacing a shower for my brother
the old one was a 8.5kw running on a 6mm cable and protected by a 32amp
just opened new shower Triton 8.5kw
added photo of consumer box and booklet
on my brothers consumer box it states do not exceed 60A
in the booklet paragraph 4.1
if its below 80A please read 4.1

and yet i took out a 8.5kw shower it has a 6mm cable protected by a 32 fuse
been working for years !!!!!
thank you Paul
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Postby Scottv3 » Tue Sep 05, 2017 8:40 pm

Hi Paul,

The 60 amp on the fuse box is purely for that RCD (bigger fuse that looks after all the smaller ones underneath it). It basically means if all those smaller fuses together pull more than 60 amps, then the RCD will trip and stop the power to them all.
The lights (from what I can) on the right by the main switch, are not protected by an RCD but that's another story.

The shower will be fine
8.5kw/240 volts = 35.5 ish amp, but this is only at full power and it is unlikely this will happen.
In theory, you could up to fuse to a 40 amp fuse but it's not needed at the 32 should be enough (as you said, it's worked up until now!)

In short, this would be fine so don't worry, the only thing I would check is that, with some older houses (like mine) there cable isn't really thick enough for the power rating. If you're cable if anything less than 10mm2, I would possibly suggest upgrading it.

Hope this helps.

Scott
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Postby paultoolbox » Tue Sep 05, 2017 11:52 pm

thank you Scott for your help
i have double checked the cable there is 6mm cable
would it be best to replace with 10mm cable and see if i can buy a 40mcb
or see if i can buy a shower at 7.5kw
what would you say is best
thank you paul
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Postby ericmark » Wed Sep 06, 2017 7:19 am

[quote="Scottv3"]Hi Paul,

The 60 amp on the fuse box is purely for that RCD (bigger fuse that looks after all the smaller ones underneath it). It basically means if all those smaller fuses together pull more than 60 amps, then the RCD will trip and stop the power to them all. [/quote]Sorry no that is not what in the main would happen, you can get RCBO's where the device is both an overload and a RCD trip, but the one shown is simply a RCD, it will have three ratings 30 mA refers to the maximum leakage before it trips, so should trip between 15 mA and 30 mA the 60 amp refers to the maximum current it can handle without damaging the device, it will not trip at that current, there will also be a prospective short circuit current maximum this is matched to the loop impedance of the supply or let through valve of the main DNO fuse and is what the device can handle without danger although it could cause damage. [quote="Scottv3"]
The lights (from what I can) on the right by the main switch, are not protected by an RCD but that's another story.

The shower will be fine
8.5kw/240 volts = 35.5 ish amp, but this is only at full power and it is unlikely this will happen.
In theory, you could up to fuse to a 40 amp fuse but it's not needed at the 32 should be enough (as you said, it's worked up until now!)
[/quote]You should not change the protective device without knowing the capacity of the cable. With the exception of flex which should always be visible so should always be air cooled, cables have tables showing what they can carry when installed in certain ways, if the cable for example had been installed in the 1980's it could be inside a cavity wall now filled with insulation so 6 mm cable could be rated at around 27 amp, it could also be thermal setting rather than thermal plastic and could well be able to carry nearly 50 amp, one can't simply look at a bit of 6 mm cable and say what it can carry, you need to know the whole of the route of that cable. Upping a MCB or fuse size without knowing cable route could be dangerous. [quote="Scottv3"]
In short, this would be fine so don't worry, the only thing I would check is that, with some older houses (like mine) there cable isn't really thick enough for the power rating. If you're cable if anything less than 10mm2, I would possibly suggest upgrading it.

Hope this helps.

Scott
You will need[/quote]If you leave the fuse or MCB size as selected by person installing the cable, if they have done their job correctly then the trip or fuse should open before the cable is damaged. Running 35 amp through a 30 amp fuse or MCB will over time likely degrade the protective device and cause it to in years to come trip or rupture before you have finished the shower, but it should not cause a danger, because a shower is used for such a short time it is unlikely any cable will be damaged in that time or any trip will open in that time, so in the main we can get away with a small overload, however unless one is 100% sure of the route you should not alter the trip size, leave that as it is, and fit the shower, should anyone then leave the shower running the trip will open before the cable over heats.

I am not saying it is right, but it is common for a showers rating to be slightly higher than the trips rating, in the main all that means is there is a time limit to how long the shower can be used for, possibly not a bad thing anyway.
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Postby paultoolbox » Wed Sep 06, 2017 8:15 am

hi Scott thank you for your reply
i do have 6mm cable
so what would be best replace cable to 10mmvbwith a 40mcb ?
or by a shower 7.5kw
oh as you say leave it as it is as its been working for 5 years
thanks Paul
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Postby Scottv3 » Wed Sep 06, 2017 12:47 pm

Hi,

The current set up should be fine.


The 6mm cable will carry the current, (depending on how it is wired it, the 'regulations' suggest the max is from about 25 to 37 amps..). So, it should be okay. The previous shower worked so why wouldn't this one?!
And again, as previously mentioned, the switch would trip before any real damage was caused.

In regards to the overloading on the cable.. yes.. it can be done, but I personally would never feel comfortable doing it if I had the ability to upgrade my cable.
While you are redoing the shower, you may as well run a 10mm cable in, this also future proofs things in case you were to upgrade in the future.


In short.. you would be fine (from what you've mentioned) to just leave it, but if it were me, I would put a 10mm cable in. I would leave the 32 amp switch though as it's incredibly unlikely that the shower would trip it.

Of course, if you ever want anything doing, it's always worth consulting a sparkie. I personally am not qualified, I just have a lot of experience (studied physics as a student and also through doing houses myself!) :)
Any more questions, please shoot :)
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Postby paultoolbox » Sun Sep 10, 2017 12:28 am

thank you Scott for your advice i`m replacing the 6mm cable with a 10mm cable leaving the 32 fuse
thank you Paul
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Postby BLAKEY1963 » Sun Sep 10, 2017 10:17 am

paultoolbox

Get in an electrician to test and inspect the work for you.
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Postby paultoolbox » Tue Sep 12, 2017 8:41 pm

good news i think !
opened the consumer box to run 10mm cable
the last sparky got his fuses mixed up !!!!
i put the shower off it was still LIVE
he wrote shower but in fact it was the cooker on a 32amp
so the shower now has a 45amp and a 10mm cable
thank you paul
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