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C'mon, let us in on the use of the building!
Earthing a "Portacabin"
- Thread starter Sidewinder
- Start date
Help Support Talk Electrician Forum:
Steps,
Missed your post earlier don't know why!
This is what I was thinking. MY initial thought was rod at both ends but try to get around 20 ohms max though, keep reading!
However the isntall was put in 5 years ago & I am just doing the 1st PIR.
However, again, I have been asked by the client to do the PIR as is at face value, & then "really" verify the install is compliant and will continue to be after AMD1 based on what we know at the moment (another clue).
As far as rodding at both ends, cabin OK though would need to protect from the strimmer!
House end bit of a tortuous run as believe it or not the mains comes in into the middle of the house through the floor!
The SWA goes up the hall in trunking and out through the wall adjacent to the front door. There is a plastic adaptable box there so I could break out & then rod from there, but, there is a serious concrete path in front of the house & I don't know which way the incoming mains goes it's this way somewhere? i.e. towards the road if "normal"
DNO probably won't know either, or they'll charge for the info!
I have been told (by DNO guys) the area supplies are all PME even though these are jointed onto the old TN-S final supply cables.
It's not bolted down as such but as I said earlier would need a road closure & BIG crane to move it anywhere over the top of the 2 storey house!
KME,
Have come to the same conclusion really.
UNLESS I give it an unsatisfactory then it will be unlikely that there will be any remedials.
Could move the RCD to the local board (ABB) with a bit of jiggling & a new RCD if wanted. Zdb is prob low enough to allow no RCD at supply end of sub main. Also all surface trunking & armoured. Armour is earthed to local "MET" at both ends & they are connected by a 16mm core as well.
NOW the crux of it, its actually a Group 1 medical Location!!!
This is coming into 7671 in AMD1.
The cabin is owned by the local health trust.
There in the requirements get a bit different, I'm hoping to get the HTM's tomorrow or at least request them, if they can get them to me.
I've done the PIR, "Satisfactory" have not commented on the earthing, only a code 4 for the RCD. Prob OTT with that really.
I do need to look further into this for them though. They have lost a lot of people and all of the electrical staff who originally worked on the concept etc. have gone. I am doing other works for them & they have started asking me to do this and to look into the situation as is now and will be (as far as we know at the moment).
There is a section in GN7 on medical locations, and the MAIN requirements are very low values of earth to the local earthing point to get disconnection times of 0.3 sec for TN systems.
HOWEVER, this is NOT yet in the regs & I have been asked to PIR to 17th.
As an aside to investigate the rest, just because 7671 is not retrospective, it does not mean that their guidance will not be!
IF we have to rod there are about 30 of these cabins, some will be TN-S, some TN-C-S, others TT. I won't know till I get around them, another in a few weeks. Then probably one every 2 weeks to a month if all goes to plan.
We may have to look at 10mA RCD's & possibly more than one rod, I can't remember the true earth values required in GN7. Prob have to get a rod test kit for my 1653 too!
Can remember that the max earth / cpc resistance between s.o., fixed apliances, extraneous parts, & local MET etc. is 0.7 ohms all ways as it were.
I've put my GN7 to bed now!
It comes down to Alberts hate of PME & touch voltages with PME, which can carry over IF the TN-S earth resistance is too high esp with G1 & G2 meds.
They call them "patient leakage currents" they can go from "electrical parts" through the patient to earth out via the med device they are connected to.
Thanks all for your help to bounce things off!
Once I've done the next one I'll have a better idea of the general standard & IIRC this one is on a TN-C-S supply!!!
Memory fading now.
GuinnessGuinnessGuinness
Paul
Missed your post earlier don't know why!
This is what I was thinking. MY initial thought was rod at both ends but try to get around 20 ohms max though, keep reading!
However the isntall was put in 5 years ago & I am just doing the 1st PIR.
However, again, I have been asked by the client to do the PIR as is at face value, & then "really" verify the install is compliant and will continue to be after AMD1 based on what we know at the moment (another clue).
As far as rodding at both ends, cabin OK though would need to protect from the strimmer!
House end bit of a tortuous run as believe it or not the mains comes in into the middle of the house through the floor!
The SWA goes up the hall in trunking and out through the wall adjacent to the front door. There is a plastic adaptable box there so I could break out & then rod from there, but, there is a serious concrete path in front of the house & I don't know which way the incoming mains goes it's this way somewhere? i.e. towards the road if "normal"
DNO probably won't know either, or they'll charge for the info!
I have been told (by DNO guys) the area supplies are all PME even though these are jointed onto the old TN-S final supply cables.
It's not bolted down as such but as I said earlier would need a road closure & BIG crane to move it anywhere over the top of the 2 storey house!
KME,
Have come to the same conclusion really.
UNLESS I give it an unsatisfactory then it will be unlikely that there will be any remedials.
Could move the RCD to the local board (ABB) with a bit of jiggling & a new RCD if wanted. Zdb is prob low enough to allow no RCD at supply end of sub main. Also all surface trunking & armoured. Armour is earthed to local "MET" at both ends & they are connected by a 16mm core as well.
NOW the crux of it, its actually a Group 1 medical Location!!!
This is coming into 7671 in AMD1.
The cabin is owned by the local health trust.
There in the requirements get a bit different, I'm hoping to get the HTM's tomorrow or at least request them, if they can get them to me.
I've done the PIR, "Satisfactory" have not commented on the earthing, only a code 4 for the RCD. Prob OTT with that really.
I do need to look further into this for them though. They have lost a lot of people and all of the electrical staff who originally worked on the concept etc. have gone. I am doing other works for them & they have started asking me to do this and to look into the situation as is now and will be (as far as we know at the moment).
There is a section in GN7 on medical locations, and the MAIN requirements are very low values of earth to the local earthing point to get disconnection times of 0.3 sec for TN systems.
HOWEVER, this is NOT yet in the regs & I have been asked to PIR to 17th.
As an aside to investigate the rest, just because 7671 is not retrospective, it does not mean that their guidance will not be!
IF we have to rod there are about 30 of these cabins, some will be TN-S, some TN-C-S, others TT. I won't know till I get around them, another in a few weeks. Then probably one every 2 weeks to a month if all goes to plan.
We may have to look at 10mA RCD's & possibly more than one rod, I can't remember the true earth values required in GN7. Prob have to get a rod test kit for my 1653 too!
Can remember that the max earth / cpc resistance between s.o., fixed apliances, extraneous parts, & local MET etc. is 0.7 ohms all ways as it were.
I've put my GN7 to bed now!
It comes down to Alberts hate of PME & touch voltages with PME, which can carry over IF the TN-S earth resistance is too high esp with G1 & G2 meds.
They call them "patient leakage currents" they can go from "electrical parts" through the patient to earth out via the med device they are connected to.
Thanks all for your help to bounce things off!
Once I've done the next one I'll have a better idea of the general standard & IIRC this one is on a TN-C-S supply!!!
Memory fading now.
GuinnessGuinnessGuinness
Paul
spinlondon
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I would suggest you refer to BS7340.
I would also suggest you contact the DNO, as some DNO's allow PME to single metal framed buildings for use by a single customer.
I would also suggest you contact the DNO, as some DNO's allow PME to single metal framed buildings for use by a single customer.
Larnacaman
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If you let me know what they intend using these portacabinss for, i might be able to help you out with any queries you may have. Many of those oversea projects i've been involved with have been hospital projects. So i've spent many years working to hospital specifications and know the various types of medical room requirements.....
But it's very late here now and i'm off to climb those stairs to my bed...lol!!!!
But it's very late here now and i'm off to climb those stairs to my bed...lol!!!!
Spin,
You mean 7430?
Mine is elsewhere at the moment however, it is on the list to find tomorrow.
I have "privileged" info on knowing the local DNO net is PME, if anyone else went to the location then the presentation is TN-S so no bother then.
---------- AUTO MERGE Post added at 01:02 ---------- Previous post was at 00:59 ----------
Larnacaman,
I did not put the exact use up immediately as I felt it may have swayed thoughts.
The PIR was to 7671 at this time.
It will have to be looked at in the future in accordance with the current UK HTM's
Which I am hoping the trust will get to me today!
You mean 7430?
Mine is elsewhere at the moment however, it is on the list to find tomorrow.
I have "privileged" info on knowing the local DNO net is PME, if anyone else went to the location then the presentation is TN-S so no bother then.
---------- AUTO MERGE Post added at 01:02 ---------- Previous post was at 00:59 ----------
Larnacaman,
I did not put the exact use up immediately as I felt it may have swayed thoughts.
The PIR was to 7671 at this time.
It will have to be looked at in the future in accordance with the current UK HTM's
Which I am hoping the trust will get to me today!
you have obviously not seen the DNO at work. seen many cases where they have done a repair or extra joint to TNS cable, bonded neutral & earth together at the join, and taken a new feed as TNCS.
now although at the existing property, it may be presented as TNS, it isnt really TNS, and could be argued it should be treated as TNCS.
you have obviously not seen the DNO at work. seen many cases where they have done a repair or extra joint to TNS cable, bonded neutral & earth together at the join, and taken a new feed as TNCS.
now although at the existing property, it may be presented as TNS, it isnt really TNS, and could be argued it should be treated as TNCS.
But I don`t think you can "second-guess" the DNO on this - irrespective of what you KNOW to be the case; you have to work on the presentation provided; NOT on your assumption of the network configuration behind it..........
Or am I wrong??
Or am I wrong??
But I don`t think you can "second-guess" the DNO on this - irrespective of what you KNOW to be the case; you have to work on the presentation provided; NOT on your assumption of the network configuration behind it..........
Or am I wrong??
Or am I wrong??
KME I think you are right in this aspect.
KME I think you are right in this aspect.
Manator
©Honorary Essex Boy™
Very good advise, assumptions have no place in the safe working methods of todays H&S driven work places.
Manator
©Honorary Essex Boy™
Very good advise, assumptions have no place in the safe working methods of todays H&S driven work places.
thats the problem, isnt it.
you may know it has a TNCS join outside property, but since its in the house as TNS, you have to pretend its TNS.
dont forget the thread the other day (steptoe?) about the PME warning label
thats the problem, isnt it.
you may know it has a TNCS join outside property, but since its in the house as TNS, you have to pretend its TNS.
dont forget the thread the other day (steptoe?) about the PME warning label
Canoeboy,
Why the groan?
Seems an odd thing to do to an OP?
Why the groan?
Seems an odd thing to do to an OP?
Canoeboy,
Why the groan?
Seems an odd thing to do to an OP?
Why the groan?
Seems an odd thing to do to an OP?
TOTD?
TOTD?
ROTFWLROTFWLROTFWLROTFWLROTFWLROTFWL
