UK SPD and AFDD practical experience

[efabian]

HI I am looking at a job where the CU needs an upgrade as its plastic and has no spare ways for the circuit I will be installing. Looking at giving customer options so will be quoting for metal CU, integral SPD and looking at combined RCBOs and AFDDs for each circuit, looking at the spec for various manufacturers minimum arc current is 2.5A. Does that preclude fitting them to lower current draw circuits such as lights as cost of devices are high at present. Is there a benefit in fitting them to every circuit?

 

[radiohead]

I have fitted AFDD's in a large historic country house with sound but old wiring, mainly as a fire risk reducing measure.
They were fitted to all final circuits including lighting, I assume you refer to lighting circuits as they are protected by low rated OCPD's, but remember even a 6a device will take a current more than enough to start a fire for a considerable period of time, and could be very slow to disconnect an arc.
But as far as AFDD's go I see no reason to install them other than in high risk or high value premises, and they add a very significant cost which most punters wont accept.
As far SPD's go give the customer the option with an additional cost, most go for it as they are cheap enough.

 

[efabian]

I have fitted AFDD's in a large historic country house with sound but old wiring, mainly as a fire risk reducing measure.
They were fitted to all final circuits including lighting, I assume you refer to lighting circuits as they are protected by low rated OCPD's, but remember even a 6a device will take a current more than enough to start a fire for a considerable period of time, and could be very slow to disconnect an arc.
But as far as AFDD's go I see no reason to install them other than in high risk or high value premises, and they add a very significant cost which most punters wont accept.
As far SPD's go give the customer the option with an additional cost, most go for it as they are cheap enough.

Thanks Radiohead, it is a high risk building, wooden cabin with kitchen and sleeping quarters, as you say cost for AFDDs astronomical at present. Client feels he is responsible for other peoples children but don't want to rip him off fitting kit with little or no benefit, especially as the cost for these will most likely drop once we're all persuaded to fit them as standard, bit like the early metal clad CUs.
Was wondering if only small loading on a circuit would an arc be generated at a high enough value for the device to activate as even the reps I have spoken to don't always agree.

 

[radiohead]

I took our scheme guy to the job and he said it was the first time he'd come across anyone ever using AFDD's, so unless your client has money to burn I'd just stick to what everyone else is doing and just use RCBO's.

 

[pc1966]

Certainly I would say there is no reason to omit SPD now as they are cheap enough and the rising amount of electronics/LED lighting (and declining quality...) in most installations make it a worth while extra.

An all RCBO board would be my own starting point as that should cover many potential fire starting faults anyway and offers high integrity and ease of finding any faults. But the argument for AFDD is not very convincing for me just now in most cases. Certainly if you have a extra grand to spend then having a proper smoke/heat alarm installed is going to save you from far more likely sources of ignition than arcing joints!

But for high-value buildings and/or for high-risk situations (particularly flammable building, risk from mice chewing cables, people unable to evacuate easily, middle of Scotland's wilderness so likely to die of hypothermia as no other shelter if they do evacuate in pyjamas, etc) they are one additional aspect of protection.

The best thing I can thing of doing is to price out the job using something with equivalent options, say the Wylex board with SPD and RBCOs and the equivalent with thier 1-module wide AFDD/RCBO alternatives, and let the client decide.

 

[bill01803]

The area engineer said to me how would I explain the omission of a AFFD on the lighting circuit on a rewire of a thatched property, he didn’t think cost was a good answer.

 

[suffolkspark]

After watching john ward video of these on youtube, they're just not worth fitting, especially the single module ones, they plain dont work. That's my reasoning. I've stopped dual rcd boards now and have gone full type A rcbo boards with SPD.

 

[Dustydazzler]

I won’t fit dual rcd boards anymore , it’s rcbo board with spd quoted on every job..
as for arc fault devices , I personally haven’t fitted any yet

 

[Darkwood]

I won’t fit dual rcd boards anymore , it’s rcbo board with spd quoted on every job..
as for arc fault devices , I personally haven’t fitted any yet

I am doing a HMO, all flats have standard dual rcd ways and I fit a SPD and its associated mcb before the rcd devices so any high integrity board where you have you rcd sections but also a non rcd protected section will do, fitting rcbo's throughout has its benefits but adds a lot to the cost especially as you are affording a SPD as well.

 

[suffolkspark]

I am doing a HMO, all flats have standard dual rcd ways and I fit a SPD and its associated mcb before the rcd devices so any high integrity board where you have you rcd sections but also a non rcd protected section will do, fitting rcbo's throughout has its benefits but adds a lot to the cost especially as you are affording a SPD as well.

Alot of dual rcd boards seem to still have 63a or 80a rcds in them, and arent many that are type A, so that tends to drop you foul of a couple of the other newer things in the regs, unless you go HAGER or some wylex, so if full rcbo I go LEWDEN, type A rcbos for about £12, and the SPD kit is £40