Fuse ratings in garage

[scott_369]

First off sorry i know this may seem a very dumb and simple question but please bear with me as im tying to learn/understand 

Exploring the fuse box/consumer unit mcb's and rcd's in my new house.

Ive noticed in the garage is a seperate box with two old style fuse wires one 30a one at 15a 

The mcb for the garage on the main fusebox in the house is rated at 16amp

Is this normal? 

How does this work if only 16a is connected to the garage but the unit inside is rated at 30amp, will the sockets inside the garage be able to run a heavy appliance or will they only be able to pull a max 16amp? 

As you can tell im not very clued up on this sort of thing so any help is appreciated 

Thanks

 

[Doc Hudson]

Welcome to the forum Scott.   You are correct that the total load for the garage will be limited by the 16A MCB supply from the main fuse box. The question "is it normal" is probably best reworded as (a) Is it frequently found in domestic installations? answer yes, very typical of DIY or 'builders-electrics' doing their 'join a few bits up to make it work technique' and (b) Is it sensible circuit design? answer No. having a higher rated fuse further along a circuit protected by a lower rated fuse serves no functional or sensible design purpose at all. Whether the current arrangement can be improved would depend upon the sizes of the circuit cables and the supply cable to the garage. It may be that someone has done a DIY fuse box replacement, purchasing a fully equipped box from B&Q or Screwfix or Wickes etc, then found out they only had a 16A MCB left to connect the garage circuit onto. Did you have an electrical inspection carried out on the new house if so were there any observations or comments regarding the garage supply?

Doc H.

 

[Andy™]

its also possible that due to the installation methods to the garage (cable size, distance etc) that >16a MCB is not suitable to protect the supply

 

[scott_369]

Thank you for the replies. At least i sort of know whats happening.

Seems a strange thing to do but makes sense as it seems to be a ready made box and the 16amp would be all thats left. 

The garage has 3 ceiling lights boiler and a couple of sockets. 

I decided to fit the washing machine in there which now seems to cause it to trip each time. 

I will have to get someone come and check if it could be replaced with a 32amp. Is it simple for someone to do if the garage wiring is suitable thickness, length wont be an issue as it just runs through the wall to the garage fuse box on the other side.

Glad i know its safe at least even if it is only letting 16amp run.

 

[ProDave]

Thank you for the replies. At least i sort of know whats happening.

Seems a strange thing to do but makes sense as it seems to be a ready made box and the 16amp would be all thats left.

The garage has 3 ceiling lights boiler and a couple of sockets.

I decided to fit the washing machine in there which now seems to cause it to trip each time.

WHAT trips? the 16a mcb or an rcd in the main consumer unit?

I would not expect a washing machine on it's own to trip a 16a mcb, was anything else running in the garage?
 

 

[scott_369]

WHAT trips? the 16a mcb or an rcd in the main consumer unit?

I would not expect a washing machine on it's own to trip a 16a mcb, was anything else running in the garage?
 

Sorry its the rcd thats tripping whenever the washing machine is on a hot cycle not the mcbs

Then after its tripped and i put the rcd back on i seem to have problems getting the garage and the oven back on at the same time  (2 mcbs next to each other) both in the on position nothing re trips just no power getting to either or only seems to go to one

 

[steptoe]

Sounds like your mcbs may not have the busbar caged properly,

As for the RCD tripping, could either be a result of the above when the wm is drawing most of its current, or, possibly more likely, the element is in the process of breaking down to earth when hot.

Some proper testing on all of the above (at least) is required tbh. 

 

[scott_369]

Sounds like your mcbs may not have the busbar caged properly,

As for the RCD tripping, could either be a result of the above when the wm is drawing most of its current, or, possibly more likely, the element is in the process of breaking down to earth when hot.

Some proper testing on all of the above (at least) is required tbh. 

Sorry knowledge doesnt take me that far......what is the busbar likely to do if not caged correctly 

The element do you mean in the washing machine? If so don't think it is that as it works when connected via an extension lead to a socket in the house. 

 

[Andy™]

what is the busbar likely to do if not caged correctly

maybe not that dramatic, but you get the idea

 

[Murdoch]

Sounds like you need a spark ..... if the OP is considering adding much to the garage load, he may need a new cable installed!

 

[Lurch]

If so don't think it is that as it works when connected via an extension lead to a socket in the house. 

That doesn't necessarily mean it isn't faulty, and it also doesn't mean that there isn't anything wrong with the garage wiring.

It sounds like it needs a looking at by an actual electrician with the proper test equipment.

 

[scott_369]

Cheers for the replies guys appreciate it. 

I will be getting someone in to have a look im just stubborn and like to try and figure stuff out myself, plus that way i can tell them what to be looking for. 

All seems very strange that after it tripped i could get everything back on apart from the oven and garage (caused the trip) both mcbs next to each other and could only get either one on but not both for a while. Both back on for now anyway 

 

[steptoe]

Cheers for the replies guys appreciate it. 

I will be getting someone in to have a look im just stubborn and like to try and figure stuff out myself, plus that way i can tell them what to be looking for. 

All seems very strange that after it tripped i could get everything back on apart from the oven and garage (caused the trip) both mcbs next to each other and could only get either one on but not both for a while. Both back on for now anyway 

:shakehead

no no no no NOOOOOOOOO

that is one sure way to piss them off

a homeowner that knows so much then why TF doesnt he fix it himself.?!?!?!?!?!?!?!?!

 

[Murdoch]

Cheers for the replies guys appreciate it. 

I will be getting someone in to have a look im just stubborn and like to try and figure stuff out myself, plus that way i can tell them what to be looking for. 

All seems very strange that after it tripped i could get everything back on apart from the oven and garage (caused the trip) both mcbs next to each other and could only get either one on but not both for a while. Both back on for now anyway 

ha ha ha...... your bill will be higher if you try..........

 

[Andy™]

 plus that way i can tell them what to be looking for. 

:slap

 

[scott_369]

:shakehead

no no no no NOOOOOOOOO

that is one sure way to piss them off

a homeowner that knows so much then why TF doesnt he fix it 

Yea sorry that sounded a lot arsier than it meant to. I just mean so i can narrow it down a bit

Also anyone know why the two mcbs seem to work against each other (after the garage trips the rcd i can get the garage on but if i turn the oven mcb on the garage goes off and vice versa for ages eventually get them both back on)  , is this likely an issue with the fuse box itself and how it was installed? 

Going to call someone out tommorow 

 

[steptoe]

He (or she) will explain when they get there,