FCU wiring question

[Geronimo W. Christ Esq]

Hi all,

In my airing cupboard I need to install two new electrical devices :

1. a wiring centre for a central heating control system. The wiring centre has it's own 2A fuse.
2. power to a relay box for a wireless room stat. This has no fuse and clearly it is intended to be connected through an FCU.

Originally I was going to wire these off the spur for the immersion heater. However, there is a double socket on the wall immediately outside the airing cupboard, so instead I can take a spur from that through the wall. This has a small advantage in that I can still in the future isolate the immersion heater if required without also isolating the heating system.

However, I'm aware that the regs permit the wiring of only one FCU off a spur - but I need to wire two "appliances". What's the best option ?

I know that the regs allow a double socket to be taken off as a spur so I could just stick plugs with fuses on the end of my two devices and connect them that way, but there's something about that which doesn't "feel" right.

Is it permitted to connect two low-current devices like this into a single FCU ? Alternatively, is there another way ?

[Nigel Molesworth]

If that is true, it's yet another case of the law being an ass.

If you can wire a double socket, why not two FCUs?

[ARWadsworth]

All your central heating controls including power to the boiler should be isolated by one switch (FCU)

One FCU with a 3 amp fuse for both the wiring centre (if it also powers the boiler) and the thermostat.

Adam

[Geronimo W. Christ Esq]

Just the answer I needed - the one FCU will indeed cover everything. Thanks muchly.

[Geronimo W. Christ Esq]

Indeed, it's dumb. I also read that you cannot wire two single sockets, to prevent the temptation of people to subsequently change the single sockets into double sockets.

I respect the point of regs for best-practice wiring purposes, but there's really no point in trying to prevent silly people from doing silly things. If you're about to wire up something stupid, you're not likely to have looked at the regs in the first place ..

[dennis]

The regs are to cope with stupid electricians not the general public. Thats why they aren't law but just codes of practice. You don't actually need to follow them, but you may well need to prove your work is safe if you don't.

[ARWadsworth]

The single sockets may be in different rooms and may be used to power heaters. This would not be good for the cable supplying the two single sockets. It is less likely that a double socket will power two heaters.

A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools (D. Adams)

Adam

[John Rumm]

Errm, since their inclusion in the building regulations (part P) they no longer just codes of practice.

To the OP, if you need more than one accessory on a spur then the spur needs to be fused. Hence you could have a 13A FCU feeding a radial circuit of half a dozen other FCUs if it made sense for a particular application.

[dennis]

You don't have to follow the regs to satisfy building regs. However you have to prove its safe and it may be easier to use the regs..

For instance you could wire the house using armoured cable. It isn't what the regs say but it is safe and should satisfy building regs.

Or drop the circuit mcb to 20A and call it a radial? I would fit the extra FCU.

[Nigel Molesworth]

Exactly. If they had brains, they wouldn't be electricians.

[Dave Stanton]

Just wiring it using SWA does not make it safe, you could still make a botch of it using SWA, in fact even more so.

Dave

[Andrew Gabriel]

If you've ever done one of the C&G electrical courses, you'd be very frightened at just what is being trained as an electrician. You will find the class splits into two -- those with a good understanding, and the hopeless, with no one much in between. Those with a good understanding always turn out to be the heating engineers, alarm installers, telcoms engineers, DIYers, etc. The hopeless ones are usually all electricians, and in most cases, already working in their trade. Now I know there are some good electricians -- I do come across them from time to time, e.g. in this newsgroup, but it's frightening to see the volume of no-hopers also working in the trade.

However, I was speaking with an FE teacher six months ago, and his comment was that if I though that was bad, I should take a look at the Home Inspectors training, where every single one of them is a complete no-hoper. These folks were supposed to do things like SAP calculations but there's just no way. They are probably going to have to subcontract everything out.

[dennis]

And your point is?

[ARWadsworth]

Have you seen some of the young no-hopers that want to be apprentices?

16 years old and never been taught how to use a screwdriver (forget power tools they have not even seen them). What happened to woodwork and metalwork at school? Has it been phased out? They also have no go in them at all. Their parents make the phone calls and write the letters for them to electrical firms asking for an apprenticeship. Maybe firms should allow applications by text messaging, as they are good at that.

Adam

[dennis]

Not from what I have seen. Most off them can't even spell using txt spch. They don't understand computers/phones either.. if they did they would use email on a pda as its quicker, cheaper than txt even to/from mobiles.

[Dave Stanton]

Thought that was obvious. Your statement that appeared to suggest that wiring house in SWA meant it was safe thats all.

Dave

[John White]

Been there, done that, got the hair-loss.

The firm I worked for took on two trainees last year. The one I got to "assist" me damaged a ceiling by kneeling between the joists. ("You never said I had to stay on that plank")

How about a spirit-level. This lad who wouldn't have seen anything wrong with the Tower of Pisa.

The only power tool he got near was a battery drill/driver. His master stroke was using it to put in accessory screws. ("It was scratched before I started", "John the head's come off this screw")

Replaced by CDT apparently. Can't change a light bulb but will tell you everything about recycling them.

This one went - about two weeks after he started.

John

[Nigel Molesworth]

I used to work at the BBC as an engineer. Every now and then there would be an intake of "Direct Entry" engineers, those who had skipped the basic training because they had a degree.

Being new to the department, we would give them something useful to do, and the one thing we were always short of was mains leads.

So, I handed a couple of metres of flex (I tell a lie, it was yards in those days) plus a 13A plug and an XLR LNE socket to our latest recruit, BSC in Physics. "Go and wire that lot up"

Half an hour later he comes back, "Which wires go to which pins". Fair enough, LNE plugs were unique to the BBC at the time, so I show him the markings. "No", he says, "the other end". Sigh!

[Steve Firth]

Oh well, you did better than I did with a graduate engineer in a high tech company a few year ago. I laboured the need to conform to ISO9000 and for each element of work I wanted to see a written plan for that category of work before anything could proceed.

He got quite aggressive about it and said that to file a plan for what he saw as "trivial" work would degrade his status as an engineer. I told him that his personal feelings aside we all had to conform to the requirement, and left him to get on.

Later that day we had a new box arrive that needed aircraft AC power to be supplied for bench testing. Said graduate engineer was tasked with wiring up the PSU but was warned to *not* turn on power until it had been checked and documented.

Five minutes later, big bang and he ran out of the lab shouting it wasn't his fault. He'd wired it up to a 400V DC power supply then switched on, no checks.

Over and over again he kept repeating that it wasn't his fault that he'd done everything correctly, and looked baffled when I asked to see his signed authority to switch the box on.

[Dave Plowman (News)]

;-)

The BBC was actually quite late in adapting Cannon LNEs as an alternative to their D&S or later Walsall Gauge used for tech supplies.

First time I saw them when I worked at TV Centre was on Micron radio mic receivers.

ITV used them rather earlier on wall boxes for tech supplies. And Anglia decided to use them the wrong way round from everyone else...