A few questions on writing out an EIC........

[cornburn]

I've had a few conflicting opinions on filling parts of the EIC for certain installation types (mainly non-domestic submains), I'm sure many of you can set me straight though I have a couple of queries,

1. Maximum demand - This is for the whole board, where you've just added a circuit to a submain with 15 other breakers in it how would you calculate a figure for this box? The same as usual as per the OSG or different with commercial installations? Clamp meter?
2. Main bonding conductor - Where you are working on a submain that is nowhere near any extraneous conductive parts, and all services are bonded from another board, and the MET for the submain is the earth bar inside it, would you put NA in these parts on the cert or would you go round with a wander lead checking continuity on rads etc?
3. One the schedule of test results you have to fill in the Ze again. If the circuit you're working on is fed from a single phase submain, which is fed from a 3 phase submain, which is fed from a main 3 phase dis board at the origin of supply, at which point would you measure your Ze? For Zs=Ze+R1+R2 to be true you would have to measure Ze at the submain you're working on (so everything external from the origin of your circuit). The Ze measurement on the first page of the EIC is under the heading "Supply Characteristics" so this means from the closest point to the meter. Does this mean that you could have 2 different figures for Ze, one on the front page from the origin of supply and one on the schedule of tests from the origin of the circuit being worked on?

Domestic stuff is so much simpler when it's all just there in front of you! Clearing these few bits up for me would be greatly appreciated so I can move on with my life

 

[Deleted member 9648]

1. I never calculate a maximum demand figure for an existing installation,If the supply fuse is 100a that is the maximum demand I will base my figure on for the cert.....or I will put 'not ascertained' .
2. The main bonding for the installation should be recorded on the cert....this would be from the MET at the intake to the point of connection regardless of which bit of the installation you are working on.
3.There is only one Ze figure....at the origin of the installation. The reading at the DB you are working on is the Zs for the distribution circuit feeding that DB.

 

[Guest123]

I've had a few conflicting opinions on filling parts of the EIC for certain installation types (mainly non-domestic submains), I'm sure many of you can set me straight though I have a couple of queries,

1. Maximum demand - This is for the whole board, where you've just added a circuit to a submain with 15 other breakers in it how would you calculate a figure for this box? The same as usual as per the OSG or different with commercial installations? Clamp meter? Maximum Demand for the whole installation....using the figures in the OSG, diversity figures are different for domestic/commercial/industrial premesis. Most put the value of the service fuse down as technically it can draw no more than this.
2. Main bonding conductor - Where you are working on a submain that is nowhere near any extraneous conductive parts, and all services are bonded from another board, and the MET for the submain is the earth bar inside it, would you put NA in these parts on the cert or would you go round with a wander lead checking continuity on rads etc? The main bonding conductors are present in the installation, check their continuity (<0.05) and put a tick in the box. Even though thay aren't in the area you are working in they are still there.
3. One the schedule of test results you have to fill in the Ze again. If the circuit you're working on is fed from a single phase submain, which is fed from a 3 phase submain, which is fed from a main 3 phase dis board at the origin of supply, at which point would you measure your Ze? For Zs=Ze+R1+R2 to be true you would have to measure Ze at the submain you're working on (so everything external from the origin of your circuit). The Ze measurement on the first page of the EIC is under the heading "Supply Characteristics" so this means from the closest point to the meter. Does this mean that you could have 2 different figures for Ze, one on the front page from the origin of supply and one on the schedule of tests from the origin of the circuit being worked on? There is only ONE Ze reading for an installation. Ze is measured at the origin of an installation with all circuits off, main earth disconnected etc etc. What you have there is the Zs for the sub-main circuit, or Zdb as some like to call it, this is measured along with the PFC at the DB you are working on.

Domestic stuff is so much simpler when it's all just there in front of you! Clearing these few bits up for me would be greatly appreciated so I can move on with my life

Hope this helps.

 

[cornburn]

Thanks both of you, that's very helpful. Just to make sure practically I'm now looking at this correctly, on the job I would:

1)Maximum diversity - no way of ever calculating this on the whole installation so ask the site supervisor where the meter is and find the suppliers fuses. It will be 3 phase so I assume maximum demand would go down as the total of the 3 cutout fuses.

2)Try and find the MET while I'm there for the bonding. The meter is likely to be in an outbuilding feeding the main building over a gigantic SWA, so if services are 100m away on the other side of the site how would you go about measuring continuity?

3)Just measure Zs directly on the far point of the circuit and check it's roughly Zs=Zdb+R1+R2, although the Zdb measurement won't go down anywhere on the certificate.

I've seen plenty of sparks working at this site (high school) and never looking further than the board they're working on. I suppose they could have called the distributor for cutout fuse size but will they have just brushed over checking the bonding? Or maybe they could have measured a continuity between the earth bar in the submain and a nearby rad or something? I obviously want to make sure my bit is done by the book though (you know the one ) Cheers guys

 

[ian.settle1]

Thanks both of you, that's very helpful. Just to make sure practically I'm now looking at this correctly, on the job I would:

1)Maximum diversity - no way of ever calculating this on the whole installation so ask the site supervisor where the meter is and find the suppliers fuses. It will be 3 phase so I assume maximum demand would go down as the total of the 3 cutout fuses.

2)Try and find the MET while I'm there for the bonding. The meter is likely to be in an outbuilding feeding the main building over a gigantic SWA, so if services are 100m away on the other side of the site how would you go about measuring continuity?

3)Just measure Zs directly on the far point of the circuit and check it's roughly Zs=Zdb+R1+R2, although the Zdb measurement won't go down anywhere on the certificate.

I've seen plenty of sparks working at this site (high school) and never looking further than the board they're working on. I suppose they could have called the distributor for cutout fuse size but will they have just brushed over checking the bonding? Or maybe they could have measured a continuity between the earth bar in the submain and a nearby rad or something? I obviously want to make sure my bit is done by the book though (you know the one ) Cheers guys

If you are writing out a seperate test sheet for each DB then the Zdb goes where it says Ze as hyperphetically it is the impedence external to that DB

 

[cornburn]

Hi Ian

The test sheet is just for the final circuit fed from the submain, so it looks like I'll have to put the Ze down as the proper Ze from near the meter (miles away from the installation). I measured the Ze from a socket fed from next to the meter as there was nothing else to get at safely (photos below). Couldn't get much closer to the substation, it's the other side of the wall! Ze from the socket was 0.04 with a PFC of 4.8kA so that should satisfy!

I'm still stuck on the maximum demand and the bonding though, as there are no markings on the main fuses (hidden inside the distributor's box) and I can't find any MET for the installation (don't think it will be anywhere near the meter). The gas supply comes in down the road a few minutes walk away and there are many main water pipes coming in. Surely I can't be testing the bonding to all these every time I put a circuit in somewhere else on site?

I take it for the cert the maximumm demand still needs to be the maximum demand for the whole site, not maximum demand for the board the circuit is fed from (125A 4 pole isolator) I rang the DNO and they didn't even know what earthing arrangement it was, let alone fuse sizes or anything else. I've got to get the certs written out urgently by tomorrow and want them to be right, any further input would be greatly appreciated

Main cutout

Supplier's panel with meter

Meter room full of bare busbars and death

SWA Isolators feeding main site

Meter room next door to substation

Cables going out to main building

 

[cornburn]

No one got any ideas? I need to handover the cert today and main fuse and bonding info / earthing conductor size is still missing off it

 

[Notsosmart]

If you cannot ascertain the main fuse size & the enquiry to the DNO was fruitless & you have exhausted all avenues then as wirepuller suggests; I would make a statement to this effect on the cert.

By looking at the photo the earthing arrangement looks like PME but this should be labelled on the header, unfortunately the only way to determine the main earth size is by being there. ( As its a school I'm suprised there aren't any previous certs or schedules/drawings etc)

As a last resort I would try another enquiry to the DNO, this time you may get hold of someone who has some knowledge of the installation; alternatively is there a local transit garage where the DNO boys meet in the mornings, a long shot but you may well get help there.

BTW; I'm sure you know but, the switch room is not storage space & the scaffolders should remove their equipment immediately

 

[cornburn]

Thanks, it is indeed a PME as one of the control rooms has a blueprint of the site layout and shows TN-C-S incoming and only the 3 phase + N coming in from next door, it must split inside somewhere but I'm not touching those covers! I was hoping they might have some old certs about so I could copy over (not strictly the right way to do things I know but better than nothing!) Unfortunately the site guy has only just started so doesn't know where anything is.

I should be able to get into the gas meter room today so I suppose all I can do for the bonding is do a visual check assuming it's near the meter and note the size. Got my NIC assessment tomorrow so really wanted to have all this in order, guess at the end of the day if he's helpful enough I could just ask him what they'd prefer me to do in this case.

 

[Sintra]

The accessor will be only to happy to advise you when he can see the installation and see what you are up against.

 

[cornburn]

What would you put down for the main earthing conductor? As it's PME it's hidden inside somewhere with nothing on show. The meter room feeds several Ottermills, which then feed down to the boards I've worked on - at which point do I measure the CSA of the earth? Would I be best to put down 16mm as that's the earth to the board I've worked on for this certificate? I'm really stuck with which figures need to be noted and I would have thought the first bit of earth on show is once you get inside a submain, everything before that is nasty busbar stuff in the Ottermills.

Same for the bonding, it's all hidden away, the gas meter is in an outside building and feeds the school from underground. I guess the bonding will join the gas main as close as possible to where it comes into the building, and not outside where the meter is. This splits to about 12 boiler rooms around the site.

Thanks for everyone's help so far but I'm really struggling with the scale of this place, the work is no different from normal but when the main supply and distribution is so huge how do you go about filling in these bits on the cert?

 

[Cj24]

Hi I am an apprentice and would like to know if when wiring lighting via a key sw does my feed and my emergency brown go togeather with my sw going out of the bottom side of the key goin to all non emergency lights