cables size?

2011

so why should the meter be the 230v point

Because:
1) That is what the ETCI determine we should use for consumer volt drop calcs
2) The ESB commit to supplying you 230 V (within a tolerance, I can't remember what the tolerance is to be honest)
3) Only the ESB can select the cable sizes on their side of the meter

The ESB can change tap settings on their transformers to compensate for the volt drop.

2011

Is it a different requirement when its outside the house?

No, the disconnection times are the same.

Bruthal

2011 wrote: »

Because:
1) That is what the ETCI require
2) The ESB commit to supplying you 230 V (within a tolerance, I can't remember what the tolerance is to be honest)

The ESB can change tap settings on their transformers to compensate for the volt drop.

They can on their 38kv station transformers automatically for more regional load changes, but local estates is more fixed i`d say, but i take your point, i never suggested any different. But the ETCI saying our voltage point is the ESB meter as opposed to the MCB board?? Common sense is needed on that one. My original point was no need to take volt drop on MCB board tails for a 4 amp load, and i`d still stick with that, although you rightly say there may be a load already on. And also i suggested it would`t be taken into account when installing a 9kw shower, assuming 16 square tails of course.

Bruthal

2011 wrote: »

No, the disconnection times are the same.

Yes but are the impedence requirements, just curious

I suppose if the disconnection times are the same then the impedences must be.

2011

Yes but are the impedence requirements, just curious

The impedance requirements are unchanged as the disconnection time is proportional to this.

Bruthal

2011 wrote: »

The impedance requirements are unchanged as the disconnection time is proportional to this.

I know, i answered my own question there i think

Although the tripping time is inversly proportional to the impedence possibly

2011

But the ETCI saying our voltage point is the ESB meter as opposed to the MCB board??

What I am saying is that you must calculate your volt drop from the ESB meter. This is because the DB may be some distance from there.

For example:
My background is industrial. A project that I have been working on the sub board is about 300m from the main distribution board and it is aprox 200m from the site transformer ( we have a 10 kV ring main on site). When sizing cables we allow for a 2% VD from the sub board.

2011

Although the tripping time is inversly proportional to the impedence possibly

No. It is proportional. The greater the impedance the longer the time it takes to operate.

2011

Sorry Robbie, I have to put a child to bed!!

Good to talk to you

Bruthal

2011 wrote: »

What I am saying is that you must calculate your volt drop from the ESB meter. This is because the DB may be some distance from there.

For example:
My background is industrial. A project that I have been working on the sub board is about 300m from the main distribution board and it is aprox 200m from the site transformer ( we have a 10 kV ring main on site). When sizing cables we allow for a 2% VD from the sub board.

Yes but the ESB meter in a domestic installation is usually a fair bit further from the mini pilar than from the MCB board, and the cable is the same size on both sides, my experience is all industrial more or less, so i see exactly what your saying, i was just thinking along the lines of it being a domestic installation and a tiny load.

Bruthal

2011 wrote: »

Sorry Robbie, I have to put a child to bed!!

Good to talk to you

Same here, always interesting which is the idea

M cebee

robbie7730 wrote: »

The fault impedence should be fine if the cable is within the 5 percent volt drop for the load scenario and the nearest size MCB is used.

mceebe seems to have all the data on this. Is it a different requirement when its outside the house?

afaik you can rcd the circuit if the Zl(loop impedance) was too high

but it's preferable to meet the disconnection times

2011

but it's preferable to meet the disconnection times

If you want to comply with the regs you must meet the disconnection times.

M cebee

my mistake

you have to meet the disconnection times

you can supplementary bond(preferable)

if not an rcd can be used for disconnection(according to rules)-but it's not standard practice afaik

TT is all disconnected this way -obviously

Bruthal

2011 wrote: »

No. It is proportional. The greater the impedance the longer the time it takes to operate.

Yes your right again, too many glasses im lookin through tonight:)

Bruthal

robbie7730 wrote: »

Although the tripping time is inversly proportional to the impedence possibly

Ha ha i cant believe i wrote that bit, using boards with a few onboard is nearly as bad as texting in the same condition:)

seaniefr

M cebee wrote: »

afaik you can rcd the circuit if the Zl(loop impedance) was too high

but it's preferable to meet the disconnection times

ZL fault loop impedance charts on page 316/317 ET101 2008
example: MCB type 'B' 6 amp resistance measurement obtained would have to be under 6 ohms if measuring from f/b side with live & earth cores bridged at end of run. Value reduces down when size of mcb is increased. The value is the same for mcb's or rcbo's. If a 'C' type is used the value reduces to 2.5 Amps for a 6 amp mcb. So maybe locate a small mcb beside gates?

M cebee

i already corrected my error on the disconnection times:)

anyway

if you measure between L and E at the DB with the ends of the swa bridged that's your R1+R2 value(part of the fault loop)

the unknown quantity is the external loop impedance measured at the DB

the total fault loop impedance is the sum of the two(in theory anyhow)

can't see any point to an mcb at end of the swa -in theory you could have a larger mcb at DB if you made the swa a 'distribution circuit' but the mcb on the final circuit would still be governed by the Zs at the end -so no benefit that i can see

e04bf097

Also don't forget to pick the correct type of CB, it might be wise to use a C type as you will be powering motors that may require an inrush current.

M cebee

is there much inrush with those gate motors? i assumed there wasn't

c type would send the Zl down more

dave45dave

Blah , blah , blah

M cebee

can you spell any other big words:pac:

dave45dave

No but at least mine makes sense.

seaniefr

M cebee wrote: »

i already corrected my error on the disconnection times:)

anyway

if you measure between L and E at the DB with the ends of the swa bridged that's your R1+R2 value(part of the fault loop)

the unknown quantity is the external loop impedance measured at the DB

the total fault loop impedance is the sum of the two(in theory anyhow)

can't see any point to an mcb at end of the swa -in theory you could have a larger mcb at DB if you made the swa a 'distribution circuit' but the mcb on the final circuit would still be governed by the Zs at the end -so no benefit that i can see

you could also factor in the need for pier lighting or any other use a power supply at a gate might get as for the external loop impedance it is a factor but is going to be a very small figure but i guess all of this means a very big cable! (or a few of them) just curious to know how the cable is going to be buried?

M cebee

dave45dave wrote: »

No but at least mine makes sense.

spit it out-what have to you got to say

:pac:


you seem to be just a sniper

M cebee

seaniefr wrote: »

you could also factor in the need for pier lighting or any other use a power supply at a gate might get as for the external loop impedance it is a factor but is going to be a very small figure but i guess all of this means a very big cable! (or a few of them) just curious to know how the cable is going to be buried?

ya i figured after that's what you meant -the majority of the fault loop impedance is on the swa