max zs table in the osg

[Lighting]

Hi all sorry for this silly question but i cant seem to find the max Zs table for a 10A BS88-2 Fusein the osg. I can find it in the BGB table 41.4
10A = 7.19 ohms and i know to multiply it by 0.8 (7.19 x 0.8 = 5.75) for rule of thumb but i would like to find the right table in the osg

 

[Octopus]

Not all the bgb is in the osg!

 

[Farmelectrics]

Use the value in the reqs but don't forget to apply the 80% factor

 

[Andy78]

Are you sure you are looking at the right table in the BGB ? table 41.4 is for 5 seconds disconnection.

 

[Pete999]

Hi all sorry for this silly question but i cant seem to find the max Zs table for a 10A BS88-2 Fusein the osg. I can find it in the BGB table 41.4
10A = 7.19 ohms and i know to multiply it by 0.8 (7.19 x 0.8 = 5.75) for rule of thumb but i would like to find the right table in the osg

Page 122 ???? I think thats right

 

[Lighting]

Are you sure you are looking at the right table in the BGB ? table 41.4 is for 5 seconds disconnection.

Hi I'm using table 41.4 has it is for street lighting.

 

[Lighting]

Page 122 ???? I think thats right

Hi Peter999 page 122 is table c1 Application of cables for fixed wiring.

 

[Pete999]

Hi Peter999 page 122 is table c1 Application of cables for fixed wiring.

Are you using the latest OSG? the yellow one?

 

[telectrix]

yellow? i'm still on the red one. it's the same electricity whatever osg you use.

 

[Pete999]

yellow? i'm still on the red one. it's the same electricity whatever osg you use.

Page 122 table B3 not sure if that is what the op is after

 

[Lighting]

Are you using the latest OSG? the yellow one?

no I'm still using the green one

 

[Pete999]

no I'm still using the green one

Flgged mine of flea bay

 

[Engineer54]

Use the value in the reqs but don't forget to apply the 80% factor

To be honest, i've never used this 80% factor and probably never will now!!
Can't see the point of why they need to mess around with proven values that have served electrical installations well for literary donkey's years...

 

[Jonspark]

To be honest, i've never used this 80% factor and probably never will now!!
Can't see the point of why they need to mess around with proven values that have served electrical installations well for literary donkey's years...

i know your not in Britain, but if you were, surely you'd have to work to BS7671 requirements?

wouldn't not meeting these requirements constitute a C2

 

[telectrix]

the figures are given in BS7671 without the 80% correction factor. these are what i use. in winter when we are measuring @3 deg.C, not 20, should we then apply another correction?

 

[Jonspark]

the figures are given in BS7671 without the 80% correction factor. these are what i use. in winter when we are measuring @3 deg.C, not 20, should we then apply another correction?

dont know. just thought you had to apply appendix 14

 

[davesparks]

i know your not in Britain, but if you were, surely you'd have to work to BS7671 requirements?

wouldn't not meeting these requirements constitute a C2

A C2 would be the code applied to a potentially dangerous fault found on an EICR, there is no such thing on an EIC.
If he has used values other than those in the books and recorded this deviation as part of the installations documentation then as long as the testing proves that the circuit is within those values there is no problem. Bs7671 is not the be all and end all of electrical installation!

 

[Engineer54]

Perhaps i should of also pointed out that the typical Zs values measured on our projects will meet and exceed anything that's presently deemed as max Zs values...

 

[Jonspark]

A C2 would be the code applied to a potentially dangerous fault found on an EICR, there is no such thing on an EIC.
If he has used values other than those in the books and recorded this deviation as part of the installations documentation then as long as the testing proves that the circuit is within those values there is no problem. Bs7671 is not the be all and end all of electrical installation!

doesn't an earth loop impedance value greater than that required warrant a potentially dangerous fault, ergo C2?

which other values apart from the manufactures are there?

 

[Jonspark]

Perhaps i should of also pointed out that the typical Zs values measured on our projects will meet and exceed anything that's presently deemed as max Zs values...

and so they should!

 

[Engineer54]

doesn't an earth loop impedance value greater than that required warrant a potentially dangerous fault, ergo C2?

Been absolutely fine for god knows how many years, so what's suddenly changed to make previously stated accepted values now ''Potentially Dangerous''?? Answer '' ...NOTHING!!

 

[Sintra]

dont know. just thought you had to apply appendix 14

The column on the cirtificate where the value of max Zs is filled in is headed "max Zs permitted by BS7671"

 

[Jonspark]

Been absolutely fine for god knows how many years, so what's suddenly changed to make previously stated accepted values now ''Potentially Dangerous''?? Answer '' ...NOTHING!!

don't quite follow u eng, nothings changed! just saying that exceeding max zs values as given in BS7671 is a C2 is it not? or is it all FINE!!!!!!

 

[Jonspark]

The column on the cirtificate where the value of max Zs is filled in is headed "max Zs permitted by BS7671"

so you dont have to stick to the 80% rule?

I am genually interested in finding the correct answer for this, so any help is greatfully received.

 

[telectrix]

and just to muddy the waters further, manufacturers data could well give a higher figure. as long as the MCB/fuse will operate within the specified time, then bob's your dad's brother.

 

[Jonspark]

and just to muddy the waters further, manufacturers data could well give a higher figure. as long as the MCB/fuse will operate within the specified time, then bob's your dad's brother.

Thanks for that.

See Eng, you don't have to add shouty exclamation marks.

 

[Jonspark]

so, you work out your fault current which is dependant upon impedance (Zs) then look up the time characteristics data for disconnection time.

 

[Pete999]

A C2 would be the code applied to a potentially dangerous fault found on an EICR, there is no such thing on an EIC.
If he has used values other than those in the books and recorded this deviation as part of the installations documentation then as long as the testing proves that the circuit is within those values there is no problem. Bs7671 is not the be all and end all of electrical installation!

Electrical Installation Certificate EIC

 

[telectrix]

the time/current graphs in BS7671 are generic. different makes of OCPDs may well give different (better) figures.

 

[Engineer54]

don't quite follow u eng, nothings changed! just saying that exceeding max zs values as given in BS7671 is a C2 is it not? or is it all FINE!!!!!!

Think about it for a second, previously stated max Zs values satisfied ADS requirements, so how can you, (or should i say they) now say that they Don't??

Of all the things that needed sorting out within BS7671, max Zs values wasn't and still isn't one of them. A totally wasted Amendment opportunity all round, when you also take into account the plastic/metal CU farce!!!

 

[Jonspark]

Think about it for a second, previously stated max Zs values satisfied ADS requirements, so how can you, (or should i say they) now say that they Don't??

Of all the things that needed sorting out within BS7671, max Zs values wasn't and still isn't one of them. A totally wasted Amendment opportunity all round, when you also take into account the plastic/metal CU farce!!!

your getting ur wires crossed,(sorry for the pun) all i'm saying is that exceeding BS7671 max CURRENT Zs figures is supposed to constitute a C2??? aaaahhhhhhhhhh!!!!!!!!!!!!!!!

 

[Jonspark]

I'll use the 7671 figures, you can use what ever you want.

 

[Engineer54]

the time/current graphs in BS7671 are generic. different makes of OCPDs may well give different (better) figures.

They shouldn't do Tel, if were talking about MCB's they are built/manufactured to a common standard according to the type B / C / D, also all the time/current curves shown in BS7671 are based on the slowest operating times...

 

[Engineer54]

your getting ur wires crossed,(sorry for the pun) all i'm saying is that exceeding BS7671 max CURRENT Zs figures is supposed to constitute a C2??? aaaahhhhhhhhhh!!!!!!!!!!!!!!!

I'm not getting my wires crossed at all, i know eactly what i mean!! lol!!

 

[spark 68]

They shouldn't do Tel, if were talking about MCB's they are built/manufactured to a common standard according to the type B / C / D, also all the time/current curves shown in BS7671 are based on the slowest operating times...

Well even in BS7671 there is provision to deviate as long as the same outcome or better is achieved, it tells us this in the good book itself.

Now most sparks (me included) will just follow the book because we are not qualified to know any better, this is no reflection on our ability and knowledge in any way, this is just the level we have been trained and taught to.

I have in the past worked for firms with their own design engineers, and these people do know better, and will often deviate because they have better data, or more importantly the knowledge to interpret that data to achieve compliance in ways us mere sparks cannot do, they are also signing that design off and taking responsibility for that decision, something I suspect most ordinary sparks would not be prepared to do.

 

[Darkwood]

The BYB max zs values are in assumption the cable could have a conductor temp' up to 70'c to which it is rated to be usable, when we test the conductor has vitually no load and thus will be at ambient Temp' this is why an adjustment is made for testing to allow for this difference, the OSG has already been adjusted for average ambient Temp' but the regs give values to cover many situations in industrial where conductor temps may well be higher so it give the opportunity for you to know the absolute max at 70c so you can taylor your calcs to suit.

If testing at lower or higher temp's than ambient then the OSG values need adjusting to reflect the difference and the BYB need to have the correct calc applied for the testing ambient temp.... if the cable is subject to any temp' variation say going through a warmer or cooler area during testing like say a fridge or proving room then it will need to be taken into account.

If you do not bother to adjust your values and just stick to the BYB max values then your circuit may not be meeting permitted trip times while under load especially if we have a heatwave and the ambient temps could be 15c + higher than were tested at and 35c + if you testing in a unheated building while building a snowman in your break - the cable may suffer damage in a fault which could impear its function and at worse become a fire hazard ... all because it was tested in ignorance to what you should have had drilled into you at college.

 

[Engineer54]

You could say the same for conducting IR tests at different temperatures. It basically boils down to knowing what you're doing, and knowing when to make adjustments/allowances accordingly to the environment the installation is subject to. All this arbitrary clap trap of using a 80% factor, is for the picture book readers....

EDIT... Let's be honest here, when are you realistically ever going to see an installation with cable temperatures running anywhere near 70 C in normal/seasonal conditions?? The only time i've seen it, was under fault conditions.... Bit different if say you are talking about one of Tony's steel factory furnaces etc, but elsewhere, ...Nah!! lol!!

 

[davesparks]

The column on the cirtificate where the value of max Zs is filled in is headed "max Zs permitted by BS7671"

That column doesn't exist in the model forms, it's something which is added by companies who produce their own versions of the forms.

 

[davesparks]

don't quite follow u eng, nothings changed! just saying that exceeding max zs values as given in BS7671 is a C2 is it not? or is it all FINE!!!!!!

Zs values have changed with the daft Cmin factor which has been introduced.

Exceeding the max values given in bs7671 will warrant a C2 code unless the designer of the installation has used values from another source or has other reasons to set the max Zs higher.