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Discuss Differences between OSG and Big regs book in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

D

DanBrown

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Has anyone noticed any differences between the New ON-SITE GUIDE and the Big Red 17th Edition regs book?.
I have noticed that some max permitted zs values are different.
For example
OSG says BS EN 60898 TYPE B 32A = 1.16 ohms
and
Main 17th Regs book says BS EN 60898 TYPE B 32A = 1.44 ohms

Is it just me reading it wrong?
if im correct, which one are you supposed to be following? as their both current 2008 17th.

Thanks in advance...
 
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B

Bane

  • Thread Starter Thread Starter
  • #2
As long as your reading is not greater than 1.44 does it matter?

(Like I know what I'm talking about)
 
P

PAUL M

  • Thread Starter Thread Starter
  • #3
Has anyone noticed any differences between the New ON-SITE GUIDE and the Big Red 17th Edition regs book?.
I have noticed that some max permitted zs values are different.
For example
OSG says BS EN 60898 TYPE B 32A = 1.16 ohms
and
Main 17th Regs book says BS EN 60898 TYPE B 32A = 1.44 ohms

Is it just me reading it wrong?
if im correct, which one are you supposed to be following? as their both current 2008 17th.

Thanks in advance...
i think you will find that 1.44 bs7671 (big book ) is the max Zs while the OSG 1.15 is the corrected value for temp (80% );)
 
Last edited by a moderator:
D

Dinosaur

  • Thread Starter Thread Starter
  • #4
That is it, the RULE OF THUMB! been around for years under 16th it was 75%, now under 17th it is 80%. it is all about making an allowance for the cable warming up and therefore its resistance increasing as current flows in the cable. clever stuff ehh!
 
S

Shakey

  • Thread Starter Thread Starter
  • #5
it was like this with the 16th regs and OSG as well.

So why have they temp corrected in the OSG but not in the regs then?......:rolleyes:

Well for those of you that wish to know...(and I must presume you do), the values given in the tables are given PRESUMING that you are also going to be using Table 7.1 rather than carrying out conventional design (as you would tend to with the full regs)

So basically, you calculate your Ib, size your In (protective device) accordingly, look it up in table 7.1, pick your installation method and earthing arangements, and you will get the max cable length for your cable size - and funny old thing, if you stick to that, then your max Zs will comply with the values given in the table (if your Ze is 0.35/0.8 as appropriate), and of course if its lower, then so will be your Zs.

(apologies to anyone now egg sucking, but some of the guys are starting in college):)
 
T

tony.towa

  • Thread Starter Thread Starter
  • #6
No apologies needed Shakey.

The main difference to me is that the OSG will fit in the glove compartment of my van. :D
 
S

Spudmiester

  • Thread Starter Thread Starter
  • #7
I think the clue is in the title, On-site GUIDE !
 
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