Bit of help please.....TT - PIR

[sythai]

Hi Chaps...

Just a few questions need a bit of help on please, just completed PIR on TT system this morning:

1/ BS3871 mcbs? Code 4 ?

2/ Readings on ring : r1=0.57 rn=0.57 r2=0.20 ? Any idea what may have happened here, somebody done a bit of an alteration maybe ? Code 2 ?

3/ Zs lower then Ze, strange ? Is this possibly to do with parallel paths ?

4/ Max permissible Zs for a TT system, would I be correct in thinking I use the value from 51.4 = 1667 (there is a 30mA/100A rcd in line)

5/ The property was thatched :

cables in loft next to thatch not mechanically protected ? Any code ?
T5 fluorescent hung in loft 300mm from thatch ? Any code ?
mr16 recessed down lights in bathroom ceiling backing into loft, non fire rated - no hood ? Code 1 ?


Many Thanks Sy

 

[malcolmsanford]

Hi Chaps...

Just a few questions need a bit of help on please, just completed PIR on TT system this morning:

1/ BS3871 mcbs? Code 4 ?
Tecnically I suppose yes as they are not now included in table 41.3 and coding it a 4 is not going to fil the PIR. Personally if there were no sign of heat damage then no code for.

2/ Readings on ring : r1=0.57 rn=0.57 r2=0.20 ? Any idea what may have happened here, somebody done a bit of an alteration maybe ? Code 2 ?
Technically the schedule of Results don't as for these readings. Did you do an R1+ R2 and if yes what was those results. If i had good R1+R2 results I might not code it.

3/ Zs lower then Ze, strange ? Is this possibly to do with parallel paths ?
Well TT Ze could be anything and most like is high. Zs should be taken down as 1667 as I'm sure there must be RCD protection, if it is an old 100mA RCD the 500 ohms. But yes if there is bonding then Zs would be lower than Ze, as you are just measuring the Ze with the eartl conductor detached, but the Zs will have all earth/bonding conductors fixed.

4/ Max permissible Zs for a TT system, would I be correct in thinking I use the value from 51.4 = 1667 (there is a 30mA/100A rcd in line) As above

5/ The property was thatched :

cables in loft next to thatch not mechanically protected ? Any code ? Is it T+E. The BS 7671-2008 does not regard a thatched roof as a special location, and as the PIR is just for the BS 7671-2008 and not building regs. Do you cable comply with BS 60332-1-2?
T5 fluorescent hung in loft 300mm from thatch ? Any code ? Reg 442.4.2 deals real with spot lights or projector lamps. I would not be overly concerned with that to be honest, and if there is no sign of heat damage no code.
mr16 recessed down lights in bathroom ceiling backing into loft, non fire rated - no hood ? Code 1 ?
Again Reg 442.4.2 and I would class that as a spot light. if under 100 watt then it must be 0.5 mteres away from the thatch. I would though in a letter be advising the use of light boxes that are steel for these lights.


Many Thanks Sy

Never really done a PIR on a thatched cottage, so I maybe miles out but I'm sure the IQ will put us right

 

[sythai]

Thanks Malcolm..... R1 + R2 was 1.24 !! something not right there.

BS 60332-1-2 would that be FP cable. It's just twin and earth up there.... for some reason I thought in a thatch it had be mechanically protected against vermin

 

[malcolmsanford]

It may have to be protected against Fauna mate, as I said to be Honest i never PIR'ed a thatch cottage or even wired one lol, so i maybe right off target if i'am then i'm sorry.

 

[IQ Electrical]

Thanks Malcolm..... R1 + R2 was 1.24 !! something not right there.

BS 60332-1-2 would that be FP cable. It's just twin and earth up there.... for some reason I thought in a thatch it had be mechanically protected against vermin

1 BS 3871 MCB's -no code.

2 The r2 value is often lower on a PIR because of parallel paths, maybe through connected loads and main protective bonding.

3 Do you mean Zs is lower than Ra? That is normally the case, Ra can be say 145 Ohms, you then add in the main protective bonding to the gas and water services and the figure becomes Zs or Zdb and comes down drastically.

4 The maximum Ra is actually 1667 Ohms with 30mA protection but for stability (soil drying/freezing) it is recommended that Ra is kept below 200 Ohms. Personally, I'd rather have a deeply driven electrode at 400 Ohms than a shallow electrode at 100 Ohms.

5 The regulations cite selection of wiring systems to suit any external influences that the installation is likely to encounter. The client's insurance company and/or Local Authority may have additional requirements where thatched properties are concerned-often fire resistant containment and void smoke detection.

Modern thatches are ammonia treated as a flame retardent and also should be seed-free so rodent damage is becoming a thing of the past.

I would find it very difficult to justify installing conventional recessed downlights and again, the Local Authority may insist on enclosed, fire rated fittings.

 

[malcolmsanford]

1 BS 3871 MCB's -no code.

2 The r2 value is often lower on a PIR because of parallel paths, maybe through connected loads and main protective bonding.

3 Do you mean Zs is lower than Ra? That is normally the case, Ra can be say 145 Ohms, you then add in the main protective bonding to the gas and water services and the figure becomes Zs or Zdb and comes down drastically.

4 The maximum Ra is actually 1667 Ohms with 30mA protection but for stability (soil drying/freezing) it is recommended that Ra is kept below 200 Ohms. Personally, I'd rather have a deeply driven electrode at 400 Ohms than a shallow electrode at 100 Ohms.

5 The regulations cite selection of wiring systems to suit any external influences that the installation is likely to encounter. The client's insurance company and/or Local Authority may have additional requirements where thatched properties are concerned-often fire resistant containment and void smoke detection.

Modern thatches are ammonia treated as a flame retardent and also should be seed-free so rodent damage is becoming a thing of the past.

I would find it very difficult to justify installing conventional recessed downlights and again, the Local Authority may insist on enclosed, fire rated fittings.

On a scale of 1to 10 my reply was a good 4 lol. ..........................

 

[sythai]

3 Do you mean Zs is lower than Ra? That is normally the case, Ra can be say 145 Ohms, you then add in the main protective bonding to the gas and water services and the figure becomes Zs or Zdb and comes down drastically.

Yes sorry Zs lower than Ra, thats it.

mr16 recessed down lights in bathroom ceiling backing into loft, non fire rated - no hood ? Code 1 ?
Again Reg 442.4.2 and I would class that as a spot light. if under 100 watt then it must be 0.5 mteres away from the thatch. I would though in a letter be advising the use of light boxes that are steel for these lights.

Definitely going to advise on light boxes, think I've still got a few in my garage somewhere.

 

[sythai]

On a scale of 1to 10 my reply was a good 4 lol. ..........................

:vanish:

Both a great helps cheers guys

 

[IQ Electrical]

Normally in a high fire risk situation, you would install 300mA RCD protection but in your case (and the case of most thatched properties due to their often rural location and hence TT supplies) you have 30mA protection, a huge leap in safety terms!