Outdoor isolator installation query

[Paul D]

Hi all,

Just joined this forum whilst doing research, so thought why not ask my question directly.

I am going to have a small split system aircon unit installed for my bedroom.

It will be a modern Mitsubishi unit with a starting current of only 3.5 Amps, nominal running current of 2.9 amps and absolute maximum running current of 7.3 Amps.

For convenience, I was intended to spur off a double socket in the bedroom straight through the wall and run 2.5mm T+E in plastic conduit down to where the outdoor unit will be.
(I know a dedicated supply would be preferable, but the Consumer Unit is the other side of the house)

I will install a 4 pole rotary isolator next to the aircon unit for maintenance isolation purposes.

Question: For this type of installation, do I need to install a Fused Connection Unit between the double socket and the rotary isolator?

Thanks in advance for any advice given.

 

[telectrix]

it would be advantageous to install a double pole FCU as a means of isolation for maintenance or if the unit develops a fault.

if you're installing in conduit, why not use 2.5mm singles?

 

[Pete999]

Hi all,

Just joined this forum whilst doing research, so thought why not ask my question directly.

I am going to have a small split system aircon unit installed for my bedroom.

It will be a modern Mitsubishi unit with a starting current of only 3.5 Amps, nominal running current of 2.9 amps and absolute maximum running current of 7.3 Amps.

For convenience, I was intended to spur off a double socket in the bedroom straight through the wall and run 2.5mm T+E in plastic conduit down to where the outdoor unit will be.
(I know a dedicated supply would be preferable, but the Consumer Unit is the other side of the house)

I will install a 4 pole rotary isolator next to the aircon unit for maintenance isolation purposes.

Question: For this type of installation, do I need to install a Fused Connection Unit between the double socket and the rotary isolator?

Thanks in advance for any advice given.

No because the Evaporator (indoor unit) is fed directly from the condenser (outdoor unit) You isolate the entire system for maintenance. Isolating the indoor unit only could cause damage to the outdoor unit.

 

[Paul D]

it would be advantageous to install a double pole FCU as a means of isolation for maintenance or if the unit develops a fault.

if you're installing in conduit, why not use 2.5mm singles?

But the rotary isolator will isolate the whole lot for maintenance, what extra advantage would the FCU give?

With regards to using not using singles, it's purely because I already have a few metres of T+E laying around.

 

[Paul D]

No because the Evaporator (indoor unit) is fed directly from the condenser (outdoor unit) You isolate the entire system for maintenance. Isolating the indoor unit only could cause damage to the outdoor unit.

Yeah, I'm quite happy from an isolation point of view, knowing that turning of the rotary isolator outside would kill both units.

My main concern was whether it needed to be seperately fused as it's taken off the mains ring circuit and is feeding what is effectively a fixed piece of equipment outdoors.

 

[Pete999]

Yeah, I'm quite happy from an isolation point of view, knowing that turning of the rotary isolator outside would kill both units.

My main concern was whether it needed to be seperately fused as it's taken off the mains ring circuit and is feeding what is effectively a fixed piece of equipment outdoors.

You said in your original post that you would spur off from the Ring Final Circuit, you never intended not to fuse that spur did you? A separate circuit would be the best idea, you may find when the A /C people come to fit the system, they will require a feed directly from the CU on a separate OCPD (fuse circuit breaker)

 

[Paul D]

You said in your original post that you would spur off from the Ring Final Circuit, you never intended not to fuse that spur did you? A separate circuit would be the best idea, you may find when the A /C people come to fit the system, they will require a feed directly from the CU on a separate OCPD (fuse circuit breaker)

Well, I originally intended to fuse it, and then just wondered if it was strictly necessary as you've got an isolator for isolation purposes and the ring circuit has its own protection. The load is lower than a single 13amp socket. I just wasn't sure what 'actual' advantages it would give. (If you take away regulatory requirements)

The a/c people said they'll fit and then test on temporary supplies. I can install the permanent wiring and isolator afterwards.

 

[Pete999]

Well, I originally intended to fuse it, and then just wondered if it was strictly necessary as you've got an isolator for isolation purposes and the ring circuit has its own protection. The load is lower than a single 13amp socket. I just wasn't sure what 'actual' advantages it would give. (If you take away regulatory requirements)

The a/c people said they'll fit and then test on temporary supplies. I can install the permanent wiring and isolator afterwards.

I have to say that's a cack handed way of doing things, will you be testing the installation, do you have the right equipment, how will yo ensure the spur you intend to install is not a spur off of a spur?

 

[davesparks]

(If you take away regulatory requirements)

.

Well in that case don't worry about the fuse, or the conduit, or the T&E, just dangle a couple of bits of bare copper down the wall to it!

 

[westward10]

Connecting from a ring final circuit will require protection by a BS1363 fuse connection unit.

 

[Paul D]

Well in that case don't worry about the fuse, or the conduit, or the T&E, just dangle a couple of bits of bare copper down the wall to it!

That's a fairly silly comment. Just because something is a regulatory requirement doesn't always mean it serves a useful purpose.

In this instance I'm not sure what value the in line fuse adds, hence why I questioned it.

Please feel free to explain the fault scenario where this helps so I can understand.

 

[Paul D]

Connecting from a ring final circuit will require protection by a BS1363 fuse connection unit.

Thank you. Much appreciate the clear simple answer.

 

[Toneyz]

The switched fused spur connection unit is for overload and shock protection (although the existing ring main circuit should have RCD protection for additional protection).