Size of suppliers fuse vs RCD

[DuncanS]

Here's a scenario, I'm adding two new circuits to a mini consumer unit for my first ever NAPIT inspection... Just noticed that the main switch/RCD is rated to 100amps but the suppliers main fuse is only 80amp, should I change the RCD to one that's 80amp or lower, I don't want the NAPIT spark to think I've over looked anything...
just to add detail the circuits on the board are as follows, oven 32amp breaker! shower 45amp breaker, jacuzzi 20amp breaker.

 

[mechelec]

oh aye..?

and what crown`s that then?

no-one comes near me in here for spite...

its not so much a crown more of a purple helmet.

 

[DuncanS]

I appreciate diversity but not so much with a shower, they draw full load from the start, at least that's what my osg tells me...

 

[trev]

I appreciate diversity but not so much with a shower, they draw full load from the start, at least that's what my osg tells me...

OSG is right. That's why you cannot apply diversity to an instantaneous water heater.

 

[DuncanS]

Yup it's the flow of water that causes temperature changes I believe, rather than a rheostat..

 

[trev]

Correct mate, that's why I laugh at people who buy megawatt showers thinking it's somehow better than say a 7.6Kw job. Your skin can only take so much heat comfortably.
Madness I tell thee, madness

 

[Meggerman]

It can routinely carry 100a, which was my concern in the first place, because if some spark has put this in some time ago and, there I go drawing 100a through it I'm gonna blow the main fuse, which would be a bugger as the DNO get funny about people just replacing them, no?
I appreciate those of you with sensible replies, for the trolls, let me remind you that once you were new to this and for me this is the first install I've done unsupervised so please do excuse my nerves, I'd rather come on here and double check my worries than leave something unsafe...

My question regarding split supply was just to confirm that this mini consumer unit you have added circuits to was not a sub main fed from main DB, which you have confirmed it is not. The important distinction you need to understand here is that the current rating of your RCD Main Switch will not limit the current you can draw through it, the installation it supplies decides that. The current rating of the RCD (in your case 100A) is the maximum it is designed to handle.

 

[mechelec]

Correct mate, that's why I laugh at people who buy megawatt showers thinking it's somehow better than say a 7.6Kw job. Your skin can only take so much heat comfortably.
Madness I tell thee, madness

But will a higher wattage shower not give the same temperature as a lower wattage one only with a proportionally higher water flow ?

 

[Meggerman]

Correct mate, that's why I laugh at people who buy megawatt showers thinking it's somehow better than say a 7.6Kw job. Your skin can only take so much heat comfortably.
Madness I tell thee, madness

In deep winter with almost freezing water supply, I'd take the 10.8Kw Mira Sport every time

 

[trev]

But will a higher wattage shower not give the same temperature as a lower wattage one only with a proportionally higher water flow ?

Perhaps, but it's still governed by the pressure of the incoming water supply

 

[Meggerman]

But will a higher wattage shower not give the same temperature as a lower wattage one only with a proportionally higher water flow ?

The more powerful the shower, the higher the volume of water it can heat as it passes though

 

[trev]

In deep winter with almost freezing water supply, I'd take the 10.8Kw Mira Sport every time

Why? The water coming out of the head is still only as hot as your skin can take.

 

[trev]

The more powerful the shower, the higher the volume of water it can heat as it passes though

See above, if the incoming flow rate is X on a 7.6 Kw it's still going to be the same on a 10Kw job

 

[Meggerman]

See above, if the incoming flow rate is X on a 7.6 Kw it's still going to be the same on a 10Kw job

The flow will be the same, but hotter for the same flow on the more powerful shower. In the winter you have to really reduce the flow rate on lower powered showers unless you don't mind it cool

 

[mechelec]

Perhaps, but it's still governed by the pressure of the incoming water supply

It's flow you need as well as pressure. 100 psi at 1 litre a minute is useless but 26 psi at 26 litres a minute will give you a great shower if it has a high enough wattage shower.

 

[trev]

The flow will be the same, but hotter for the same flow on the more powerful shower. In the winter you have to really reduce the flow rate on lower powered showers unless you don't mind it cool

But you're still only going to have it as hot as you can stand. Are you seriously telling me that you can't get a hot enough shower on a cold day from a relatively low powered one compared to that Mira you mentioned?
When I was playing rugby the showers were never switched on anyway so I kind of got used to cold showers. Nowt to do with spanking the monkey mind you