Would it not be the case that the GY entering the top of the MET is the MEC and is connecting all the exposed conductive and extraneous conductive parts to the means of earthing, ie the DNO braid in this instance.
Would it not be the case that the GY entering the top of the MET is the MEC and is connecting all the exposed conductive and extraneous conductive parts to the means of earthing, ie the DNO braid in this instance.
D
davesparks
Would it not be the case that the GY entering the top of the MET is the MEC and is connecting all the exposed conductive and extraneous conductive parts to the means of earthing, ie the DNO braid in this instance.
MEC?
The earthing conductor is the consumers conductor which connects the MET to the means of earthing. In this case the distributors means of earthing connects directly to the MET.
Any installation can only have one earthing conductor, just as there can be only one MET
Ok, which would you put down on an EIC as the earthing conductor, the GY or the braid?
I meant main earthing conductor. Got my terminology slightly mixed for a moment there!
I meant main earthing conductor. Got my terminology slightly mixed for a moment there!
D
davesparks
Neither, I'd record it as N/A with an explanatory note.
I know what you meant, it was just a polite nudge that that term doesn't exist in 7671, it's just the earthing conductor.
Cool thanks for pointing that out. I was getting mixed up with Main protective bonding and earthing for a minute there.
D
davesparks
It seems petty I know, but in a technical trade accuracy is important
N
newtothis
Yes it makes sense, I'm trying to figure out how you got the value for t.
(1) I know I'm supposed to look up those graphs - but I don't know which one is applicable.
Is it the main protective overcurrent device, or if you don't mind naming the page in appendix three.
Thanks for your patience
D
davesparks
Yes it makes sense, I'm trying to figure out how you got the value for t.
(1) I know I'm supposed to look up those graphs - but I don't know which one is applicable.
Is it the main protective overcurrent device, or if you don't mind naming the page in appendix three.
Thanks for your patience
Value for t is, as you say, obtained from the graphs in the appendix.
Figure 3A3(a) on page 322 is where I got it from.
N
newtothis
Great thanks
N
newtothis
TBH I was giving the adiabatic equation (AE)a wide berth - I’m well pleased to be on the verge of understanding thanks to the help on this forum.
The first time I looked at these graphs, I just saw some kind of confusing spiders web.
I’ve sussed how the scales work. I’m posting it up here to check I’m using the graphs correctly.
Starting with my 900A PFC on the horizontal axix
Going up to crossing line
Then across to the vertical axis (time)
I’m getting 0.2 rather than 0.6 for “t”, is my methodology wrong ?
Plugging the t value into the (AE) I get 2.8
Taking this further, If I was to check the required CSA of CPC on a final circuit I’d use the Zs rather than the ZE I’ve used in this example ?
The first time I looked at these graphs, I just saw some kind of confusing spiders web.
I’ve sussed how the scales work. I’m posting it up here to check I’m using the graphs correctly.
Starting with my 900A PFC on the horizontal axix
Going up to crossing line
Then across to the vertical axis (time)
I’m getting 0.2 rather than 0.6 for “t”, is my methodology wrong ?
Plugging the t value into the (AE) I get 2.8
Taking this further, If I was to check the required CSA of CPC on a final circuit I’d use the Zs rather than the ZE I’ve used in this example ?
D
davesparks
Yes you are using the graph correctly, but that doesn't look like the same graph as I was looking at.
I'll have a look in my regs book when I get home and get back to you.
L
Leesparkykent
Is that the graph for bs88-3? I don't have my BYB on me. But Davesparks must of been lookin at the graph for bs88-2 I think.
N
newtothis
Thanks I've checked it out, and think know what table Davesparks used. 3a3(b)
I used 3a3(a)
I need to learn up about what graph to use.
I think you experinced sparks can look at the fuse even tho it's not labled up and know what graph to use - I can't.:44:
I used 3a3(a)
I need to learn up about what graph to use.
I think you experinced sparks can look at the fuse even tho it's not labled up and know what graph to use - I can't.:44:
N
newtothis
All that's on the DNO fuse is "lucy oxford", I happen to know it's a 60a fuse.
No way would I be able to suss the BS no of it ? :sad_smile:
No way would I be able to suss the BS no of it ? :sad_smile:
Lucy house service cut outs (as most of them) are designed to accept BS1361 fuses, because BS1361 has now been withdrawn and replaced with BS88-3:2010, therefore you should look at the graph for BS88-3 (type C) fuses.
However there is also the problem that the standard fuse ratings have changed a bit so a 60A BS1361 standard rating is now a standard rating of 63A in BS88-3, which really does not help much.
Grab the red book and use the BS1361 graphs!
Then you would find the fusing time at about 900A would be about 0.095 s slightly slower than the just off graph possibly 0.07 s of the 63A in BS88-3.
However there is also the problem that the standard fuse ratings have changed a bit so a 60A BS1361 standard rating is now a standard rating of 63A in BS88-3, which really does not help much.
Grab the red book and use the BS1361 graphs!
Then you would find the fusing time at about 900A would be about 0.095 s slightly slower than the just off graph possibly 0.07 s of the 63A in BS88-3.
N
newtothis
Thanks,
Hmmm who carries all those books LOL, unfortunaley I've only got the green and yellow.
Is there anything (an alternative method) like a table in the OSG that would work.
Hmmm who carries all those books LOL, unfortunaley I've only got the green and yellow.
Is there anything (an alternative method) like a table in the OSG that would work.
L
Leesparkykent
......
Attachments
D
davesparks
Based on the above couple of posts I apologise for my above posts which are incorrect. I was basing my calculations on a 100A bs88-2 fuse.
Would somebody please pass me the dunce's hat, I'll be over in the corner.
Would somebody please pass me the dunce's hat, I'll be over in the corner.
N
newtothis
Leesparkykent - that wouldn't be the relevant graph from the BRB by any chance LOL ?
On a side note have I got a case for asking the DNO to upgrade the cut out ?
I been taught about asking for Ze by enquiry and stuff.
The reality with my DNO UKPN is they're not interested in anything that isn't an earner for them.
On a side note have I got a case for asking the DNO to upgrade the cut out ?
I been taught about asking for Ze by enquiry and stuff.
The reality with my DNO UKPN is they're not interested in anything that isn't an earner for them.
N
newtothis
No mate, no dunces hat because you've taught me useful stuff I couldn't understand before. It's my responsibility to check, understand and do my own learning, not to be spoon fed, by good people like yourself and others who help.
The table in the top right shows that a 63 A will operate at 0.1 s at 820 A, so you can say at 900A it would be faster but if you take 0.1 s this will give a higher csa in the adiabatic if you then calculate for the earthing conductor and get a csa that is less than what you have at present then you are OK.
e.g. result is 2 mm² you have 6 mm² no problem.
e.g. result is 2 mm² you have 6 mm² no problem.
L
Leesparkykent
......
N
newtothis
Thanks for the image.
The coin has dropped - I'm feeling very happy !
Before this I couldn't even read the graphs :rolleyes4:
And I gave the adiabatic a major body swerve.
I fairly confident I can consolidate what I've learned from this post and take it further.
The coin has dropped - I'm feeling very happy !
Before this I couldn't even read the graphs :rolleyes4:
And I gave the adiabatic a major body swerve.
I fairly confident I can consolidate what I've learned from this post and take it further.
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