First Commercial Periodic Inspection *Update*

[sparky05084]

Hey peeps!

First of all hoping you all had a sound bank holiday weekend (mine was obviously working and earning the pennies but hey ho).

Secondly, apologies if I should simply be replying to my previous thread rather than making a new one. Hope I’m not breaking any rules moderators. Just assumed that the thread had been closed.

Okay, thanks to the guys for advise regarding IR testing the lighting circuits – you know the L/N – CPC method. I must admit though, the guy that mentioned frying something and having to bull his way out of it really got me going lol. Was really cautious and things seemed to take ages like double and even treble checking things.

I must have checked the IT equipment in the office was all unplugged 20 dozen times. I was ssssoooo slow on this job. Glad I did it on day rate

Now, I am in the process of sorting the customers invoice and writing his certificate(s). However and as per usual I am a little stuck and in need of some much needed help. This is a very first for me so please bear with me as I cannot make a mistake and this guy has promised me future work so I want to make the best possible impression. Basically rather than go on and on (which I might add I tend to do ) I will simply ask the questions in order.

Please bear in mind there are quite a lot of them and I am quite prepared to be told how to “suck eggs” and yes I admit some questions are leaning on the lazy side so please don’t just answer “go and look yourself”. I have done so with OSG and regs but want to be absolutely sure. I appreciate sometimes looking yourself and finding out is the process of learning and what makes a good spark but I don’t want to make any mistakes and I want this cert to be A1.

Thanks guys in advance and I hope you can help me.

Regards

Sparky05084

Q1. The main incomer is a three phase TNC-S 415V supplying three phase board to final circuits which are:

3x 16A 60898 C type three phase, neutral and cpc sockets
1x 63A 60898 C type single phase sub main supply to office
1x 32A 61009-1 C type workshop ring main (3x twin sockets metal clad)
1x 16A 61009-1 twin socket outlet metal clad
1x 10A 60898 C type alarm supply
1x 6A 60898 C type workshop lights (6 x twin florescent fittings)

With regards to RCD protection, previously, the workshop ring main was just protected by a standard 32A 60898 B type MCB as was the single twin socket outlet (radial) by 16A 60898 type B MCB. I have changed these for RCBO’s to afford RCD protection. As the three phase sockets are unique and clearly labelled and meant for only one item of equipment then I do not need to have these circuits RCD protected? What about the alarm and lighting?

Q2. The Ze at the origin of supply was measured at 0.14Ω. When I got on to testing the office board I got a measurement for Ze at 0.29Ω. In the details at distribution, consumer unit section (ethos booklet) it is asking in “system characteristics” for Ze/Zs. Do I simply put 0.29 or would I deduct the original 0.14 at origin? Also, on previous periodic where test cert has been wrote out for DB2 (office), the supply type is recorded as TNS. Basically the C63A MCB in three phase board is protecting 16mm T+E that goes to office board. Is then to put TNS correct?

Q3. With regard to the RCBO’s for workshop ring main and radial twin socket, are the maximum permissible trip times the same where a 30mA RCD is concerned so 1x 200mS and 5x 40mS? I heard somewhere that for 61009-1 RCBO’s up to 32A that 5x is 150mS or am I completely mistaken?

Q4. I believe that 0.4 seconds disconnection time is compulsory now but I am a little unsure. What are then the max disconnection times for these?

16A 60898 C type three phase – these are fixed equipment so 5secs?
63A 60898 C type – sub supply to office board
32A 61009-1 C type and B workshop/office ring main
16A 61009-1 C type and B workshop/office radial sockets
10A 60898 C type – alarm
6A 60898 C – lights

Q5. Going back to supply characteristics I am presented with this for fault level(s) for my PEFC/PSCC readings.
1 f
3 f
Erm lol. I got my reading at origin (three phase board) at 2.4kA, 0.72kA at office board. Measured with Megger MFT 1553 tester if helps at all. As I am supplying 2 separate sheets for each individual board and circuits then what is the 3 f for? I put my three phase reading in there and then the single phase reading in 1 f?
Am I missing something?

Q6. Extent of electrical installation covered by this report. I am going to write in “entire”. Is this correct?
Also, in small print in extent and limitations box at bottom it states “ This inspection has been carried out in accordance with BS 7671:2008 (IEE Wiring Regulations), amended to……..blar blar blar. The……indicates a blank space. Do I put 17th edition in here?

Q7. Finally, this is one for you experts and I will either (a) get laughed at and ridiculed for missing something completely obvious or (b) will be a stumbling block or a genuine fault. During IR testing at 3 phase board I did my 10 step tests as you do. I got to N – E and immediately got a dead short (0.00MΩ). So, I was like ok that’s not supposed to happen. Removed all the outgoing neutrals and tested between N – E bars again. Still dead short. Now I got myself thinking it’s a TNC-S system so neutral and CPC are common. Is that why I’m getting the reading? Removed the main incoming 16mm earth (don’t ask why was just clutching at straws now ). I even isolated as stated in safe isolation but building was empty anyway. Good practise don’t you think? Tested again and still getting a short. All the neutrals had been removed one by one and tested each time I removed one from bar so why am I getting a short between N – CPC??

 

[Deleted member 9648]

Hey peeps!

First of all hoping you all had a sound bank holiday weekend (mine was obviously working and earning the pennies but hey ho).

Secondly, apologies if I should simply be replying to my previous thread rather than making a new one. Hope I’m not breaking any rules moderators. Just assumed that the thread had been closed.

Okay, thanks to the guys for advise regarding IR testing the lighting circuits – you know the L/N – CPC method. I must admit though, the guy that mentioned frying something and having to bull his way out of it really got me going lol. Was really cautious and things seemed to take ages like double and even treble checking things.

I must have checked the IT equipment in the office was all unplugged 20 dozen times. I was ssssoooo slow on this job. Glad I did it on day rate

Now, I am in the process of sorting the customers invoice and writing his certificate(s). However and as per usual I am a little stuck and in need of some much needed help. This is a very first for me so please bear with me as I cannot make a mistake and this guy has promised me future work so I want to make the best possible impression. Basically rather than go on and on (which I might add I tend to do ) I will simply ask the questions in order.

Please bear in mind there are quite a lot of them and I am quite prepared to be told how to “suck eggs” and yes I admit some questions are leaning on the lazy side so please don’t just answer “go and look yourself”. I have done so with OSG and regs but want to be absolutely sure. I appreciate sometimes looking yourself and finding out is the process of learning and what makes a good spark but I don’t want to make any mistakes and I want this cert to be A1.

Thanks guys in advance and I hope you can help me.

Regards

Sparky05084

Q1. The main incomer is a three phase TNC-S 415V supplying three phase board to final circuits which are:

3x 16A 60898 C type three phase, neutral and cpc sockets
1x 63A 60898 C type single phase sub main supply to office
1x 32A 61009-1 C type workshop ring main (3x twin sockets metal clad)
1x 16A 61009-1 twin socket outlet metal clad
1x 10A 60898 C type alarm supply
1x 6A 60898 C type workshop lights (6 x twin florescent fittings)

With regards to RCD protection, previously, the workshop ring main was just protected by a standard 32A 60898 B type MCB as was the single twin socket outlet (radial) by 16A 60898 type B MCB. I have changed these for RCBO’s to afford RCD protection. As the three phase sockets are unique and clearly labelled and meant for only one item of equipment then I do not need to have these circuits RCD protected? What about the alarm and lighting?No and no...with regard to buried cables needing RCD protection this would be a code 4

Q2. The Ze at the origin of supply was measured at 0.14Ω. When I got on to testing the office board I got a measurement for Ze at 0.29Ω. In the details at distribution, consumer unit section (ethos booklet) it is asking in “system characteristics” for Ze/Zs. Do I simply put 0.29 or would I deduct the original 0.14 at origin? Also, on previous periodic where test cert has been wrote out for DB2 (office), the supply type is recorded as TNS. Basically the C63A MCB in three phase board is protecting 16mm T+E that goes to office board. Is then to put TNS correct?0.29 will be the Zs at the office DB.....if it is TNCS at the origin it will be the same at the office DB

Q3. With regard to the RCBO’s for workshop ring main and radial twin socket, are the maximum permissible trip times the same where a 30mA RCD is concerned so 1x 200mS and 5x 40mS? I heard somewhere that for 61009-1 RCBO’s up to 32A that 5x is 150mS or am I completely mistaken?200/40 as far as I'm aware

Q4. I believe that 0.4 seconds disconnection time is compulsory now but I am a little unsure. What are then the max disconnection times for these?
0.4s for all final circuits....5s for distribution circuits,
16A 60898 C type three phase – these are fixed equipment so 5secs?
63A 60898 C type – sub supply to office board
32A 61009-1 C type and B workshop/office ring main
16A 61009-1 C type and B workshop/office radial sockets
10A 60898 C type – alarm
6A 60898 C – lights

Q5. Going back to supply characteristics I am presented with this for fault level(s) for my PEFC/PSCC readings.
1 f
3 f
Erm lol. I got my reading at origin (three phase board) at 2.4kA, 0.72kA at office board. Measured with Megger MFT 1553 tester if helps at all. As I am supplying 2 separate sheets for each individual board and circuits then what is the 3 f for? I put my three phase reading in there and then the single phase reading in 1 f?
Am I missing something?not the same forms as I use so not sure.

Q6. Extent of electrical installation covered by this report. I am going to write in “entire”. Is this correct? Yes,but specify the extent of your visual inspections,you cannot inspect it all.
Also, in small print in extent and limitations box at bottom it states “ This inspection has been carried out in accordance with BS 7671:2008 (IEE Wiring Regulations), amended to……..blar blar blar. The……indicates a blank space. Do I put 17th edition in here?You put in the date of the last amendment...1/1/08

Q7. Finally, this is one for you experts and I will either (a) get laughed at and ridiculed for missing something completely obvious or (b) will be a stumbling block or a genuine fault. During IR testing at 3 phase board I did my 10 step tests as you do. I got to N – E and immediately got a dead short (0.00MΩ). So, I was like ok that’s not supposed to happen. Removed all the outgoing neutrals and tested between N – E bars again. Still dead short. Now I got myself thinking it’s a TNC-S system so neutral and CPC are common. Is that why I’m getting the reading? Removed the main incoming 16mm earth (don’t ask why was just clutching at straws now ). I even isolated as stated in safe isolation but building was empty anyway. Good practise don’t you think? Tested again and still getting a short. All the neutrals had been removed one by one and tested each time I removed one from bar so why am I getting a short between N – CPC??The N and earth are at the same potential,you should disconnect the incoming neutral from the N bar and then test N bar to earth

Hope this helps.

 

[sparky05084]

Cheers Wirepuller!

Was a little concerned that the length of that post would put people off, alas you have replied to which I am very grateful. Ok mate I’m in the process of filling out certs as I type this. Just a few things that I would like you to elaborate on please.

With regard to your answer in Q1. I do not need to put in any codes do I as the other circuits barring the ring main and radial socket (RCBO's) are supplying fixed items of equipment (non portable) and are run in containment thus protected via mechanical means - conduit, trunking. Therefore it would not be necessary would it to put that these circuits have no RCD protection when it is not required.

For Q4 when you say 5s for all distribution circuits would you then mean for example the 63A sub feed going to office DB? I assume final circuits mean every/and other circuit leaving DB's like ring main, lighting etc? What about boiler supply, alarm, roller shutter door supply, disabled alarm supply? Not sure what to put for these.

Q6. I went a bit over board on this PIR to be honest. Perhaps because it was my first and I was faffing about. So, I did do at least 70% visual (I know I know that’s a bit OTT but hey at least I did a good job). I simply put here then "visually inspected 70% of accessories and equipment. Internally inspected 70% blar blar" is that correct?

Q7. Ah ha! So I made a mistake. Oh well, we all learn I suppose a bit embarrassed but thanks for pointing that out to me I must remember that for future. However can I ask this then? You said that N and CPC are at the same potential as it is a PME system and I mentioned that I removed the main incoming earth. Would this then not have the same effect as removing the main neutral? You are removing the potential by removing either N or CPC I would imagine yet I was still getting a dead short. Confused........lol

 

[Deleted member 9648]

As far as I can see the only distribution circuit is the one feeding the office DB,all the others ar finals.....you are not allowed to call them sub-mains anymore...they are distribution circuits!!lol.....A distribution circuit would be one feeding another DB.
Q6....I would normally state that a sample of points were removed for inspection,and that only accessable parts of the installation were visually inspected,this would not include cables within the fabric of the building,and within conduit/trunking etc.....Obviously if points you removed were showing problems the sample would have to be increased.
Q7....you would likely still get an earth potential via parallel paths from the connected final circuit earths,through bonding,steel conduit on structural steel etc.

 

[sparky05084]

Thanks Wirepuller. Ive noticed that you have made an effort to reply to most of my threads. Thanks!

Yes indeed you are correct and I did not consider that. The installation has gas, water and structural steel bonded as is supplementary in place so yes parrallel paths would have most likely been the scenario that was giving me that duff reading. I will remember this for next time so Im not caught off guard.

Not long since finished all the certs and other paperwork. What a chore. You know its at times like this I wonder if trying to set up shop on own is really worth it. I mean staying up till silly o'clock just to catch up on paperwork and sorting quotes out when I'd be rather watching top gear or somet else.

Oh well rant over