High ish Ze

[uksparks]

Hi

ive been at my mates today between Boston and skeggy in the middle of knowhere surrounded by cabbages.

hes on the very end of an overhead supply, it's PME.

the Ze is 0.56 ohms, would you say this is a big on the high side? I know it's on a long run and they can be high but just wondered what your thoughts were.

ivd just been putting a sub main up to some out buildings and a caravan pitch and earth rods, quite pleased as put one heap of 4 x 5/8 rods and got 5.7 ohms!

 

[LeeH]

Depends on the fuse size I guess.

Call the DNO and see what they say if you don't want use the BS7671 value.

 

[uksparks]

I'll give them a call, I suspect they will say it's remote and there's not much they can do.

 

[LeeH]

Pull the fuse and see what size it is. You may be able to go down a size load dependent of course.

If not I presume you would have to treat it like a TT?

 

[uksparks]

Hi,

What has the fuse size got to do with it?

TNS = 0.8
TNCS = 0.35
TT = 200~

Its out of parameter for the supply type? Or am i being thick and missing something?

It is a PME supply, its got an 1362 Type II b 80A fuse.

 

[uksparks]

the earth rod was at the remote end around 80 meters from the cut out where the caravan pitch was, thats the only TT bit on the installation.

I had just ran a 16mm submain from a 63A switch fuse at the cutout to the out building up the field thats all, but thats on the supply earth.

It was just the measured Ze at the switch fuse at the supply end that I felt was out of parameter, like I say i know they can be a bit higher than specified top end figures, but wasn't sure how much over you would say is acceptable.

 

[7029 dave]

If 0.56 ohms is stable, don't sweat it . If it was a tt arrangement at 200 ohms so what,stability is key. (with in reason)

 

[Risteard]

It is a PME supply, its got an 1362 Type II b 80A fuse.

The fuse must be in a very big plug top.

 

[mhar]

My youngest is a Western Power technician. For a pme connection their policy is - below 0.35 connect, between 0.35 and 0.8 to connect and advise.
Don't think you will get much joy from the dno

 

[LeeH]

Hi,

What has the fuse size got to do with it?

TNS = 0.8
TNCS = 0.35
TT = 200~

Its out of parameter for the supply type? Or am i being thick and missing something?

It is a PME supply, its got an 1362 Type II b 80A fuse.

Those are BS7671 values, not the DNO's.

They will most likely have their own.

You understand why you need low impedance for a given OCPD so the same must apply for the fuse in question shouldn't it?

Every DNO have their own rules.

 

[LeeH]

The fuse must be in a very big plug top.

Have you not seen the PME plugs?

 

[davesparks]

Hi,

What has the fuse size got to do with it?

TNS = 0.8
TNCS = 0.35
TT = 200~

Its out of parameter for the supply type? Or am i being thick and missing something?

It is a PME supply, its got an 1362 Type II b 80A fuse.

The Ze guidelines are different for different fuse sizes, it's a bit scary that you need to ask that, do you not understand the point of earth fault loop impedance?

I think from memory the guideline for an 80A supply is in the region of 0.5/0.6, but the DNO will confirm as it is dependant on their own internal guidelines.

 

[davesparks]

I had just ran a 16mm submain from a 63A switch fuse at the cutout to the out building up the field thats all, but thats on the supply earth.

Could you not get any closer to the supply terminals to do the test then? Surely you must have connected the tails to the switchfuse in to something closer?

 

[davesparks]

Those are BS7671 values, not the DNO's.

.

Where in bs7671 please?

 

[LeeH]

Where what?