Fused connection unit mounted on metal backbox

[Gary Tollison]

greetings

I’m taking a spur from a ring final.
A fused connection unit will be controlling the spur.
FCU will be mounted on a metal backbox flush in a brick wall.
I’m planning on using a junction box to break into the RFC, and taking the spur cable to the FCU.
My question is, do both cables going to and from the FCU have to be in the same hole in the back-box, or can I have each cable in a different hole?
Thanks,
Gary

 

[Andy78]

Whichever is best for the physical constraints of installation. What's your thinking behind this question ?

 

[telectrix]

why not just install 1 cable from JB to the FCU?

 

[Gary Tollison]

As there isn’t much room for both cables to go through the one hole, and putting a rubber grommet in there for both is a right pain in the proverbial, so I decided that one cable in each would easier

Telectrix, apologies for my not being very clear, I wasn’t quite awake when I typed it There will be one cable coming from the junction box to the FCU, and another coming from the FCU to supply the spur dependants



Thanks for the replies!

 

[telectrix]

i never have any trouble fitting 2 x 2.5mm cables through a 20mm hole with grommet. but no problem in using separate holes if that's your preference. ( cost you an extra grommet though. ).

 

[Octopus]

What type of junction box do you have in mind?

 

[telectrix]

are there any other types?

 

[telectrix]

ah, found one:

 

[Wilko]

I thought I got a sniff of an eddy current debate there for a moment .

 

[Deleted member 26818]

are there any other types?

Yes, they do one with four terminals.

 

[Gary Tollison]

This one I’ll be using

 

[SparkyChick]

That will need to be accessible to testing in the future. You would be better off using a maintenance free junction box, such as a Wagobox with appropriately sized and rated Wago connectors.

Or Hager do some nice maintenance free boxes.

Basically anything with a screw terminal needs to be accessible for test and inspection as over time, thermal cycling can cause the termination to loosen. Loose terminals = fire risk.

 

[Gary Tollison]

Yup, I’ve made a section of the floorboards liftable where the junction box is located nice and easy to get to

 

[SparkyChick]

Yup, I’ve made a section of the floorboards liftable where the junction box is located nice and easy to get to

Why complicate your life (and more importantly the next owners of the property). Do it properly in the first place and use a maintenance free junction box.

 

[Andy78]

I agree with SC. Although the definition of accessible is open to interpretation, I use MF connections when concealed in the fabric of a building, including under floors.

 

[Spoon]

Yup, I’ve made a section of the floorboards liftable where the junction box is located nice and easy to get to

As already mentioned above. I personally wouldn't class a junction box under the floor boards as "accessible"

 

[Gary Tollison]

It is accessible. Lift back a corner of the carpet, remove a few small precut sections of floorboards...can get to
It in less than 30 seconds.
As long as there is access to it, I don’t see the problem

 

[pirate]

There's always access...just depends on whether the next person knows where to gain that access, and how. Ah...log-books for circuits! Another debate...
If you could run the spur to the FCU and straight out again in a straight line, would that worry you?
I ask this, as a non-spark, but am thinking if we ignore the eddy current debate (Please, let's ignore that here) then the leccy will turn the corner fine! and won't care what hole it comes in and exits from...
which is also another debate we probably don't need to pursue here!

 

[Gary Tollison]

I guess it’s down to the individual’s preference
As long as I can get to it with little effort then it’s fine.
But yes, there is the need of future notification of the “how to get to it” which must be addressed.
In an ideal world there’d be a detailed map of each electrical installation, but dreams are free

 

[SparkyChick]

I guess it’s down to the individual’s preference
As long as I can get to it with little effort then it’s fine.
But yes, there is the need of future notification of the “how to get to it” which must be addressed.
In an ideal world there’d be a detailed map of each electrical installation, but dreams are free

The reason you have a choice is because of ambiguity in the regulations regarding the word 'accessible'. My personal view is if I'm not going to be able to see it when the work is completed, it's not accessible and hence it should be maintenance free. Some examples... in the kick space of kitchen cabinets, under insulation in lofts, in walls and floor/ceiling voids. In some of those cases, it can be argued that they are easily accessible... sure, they are. But to access them you need to know something is there that requires it.

Looking at your profile, you're training to be an electrician right? Well, don't take this the wrong way, but in my view what you're proposing is a bad practice... secreting a junction box that will require inspection in the future out of sight within the fabric of the building.

Doing the job properly in the first place drastically reduces the possibility of it causing issues in the future and helps make life easier for the next person to work on the installation... an approach you'll appreciate when at some point that next person is you.

With regards to there being a detailed map, that's down to the person doing the work. I try and provide such information in the form of 'as installed' plans or notes on the certificates. After that, it's down to customer keeping that information together.