volt drop

[Ian Speirs]

Was at a job today, i'll try to keep this short, Country park toilet block, 25mm 4core swa tp & n supply, armour as cpc. (TN-S main supply).

100a, 100mA 4 pole rcd at toilet block,

60A 3036 fused switched isolator at supply end, OVER 1 MILE AWAY.

3 phase required for 3 small pumps,

yellow phase used to supply 11 way 30mA rcbo filled db, max demand 40A, everything switched on votage measured at 189v at db main switch.

Zs at 100mA RCD 2.6ohms on each phase.

Was going to mearure the resistance if the cores of the supply cable and calc the distance of this run but the park manager then told me the campsite shower block and 2 water treatment tanks, (bio discs) have been tapped off this cable along the way. was getting late so called it a day at that.

I was only called to investigate nuisance tripping of the 100 mA RCD which i found after 30 mins. Took me another 4 hours to gather this mess.

Thought i'd do some volt drop calcs to get some figures for the boss, P 281 BRB shows r 1.50, x 0.145, z 1.50

How are these figures used in the VD calc? Was going to say the cable is 1 mile long till i get a more accurate measurement.

Sorry i lied about keeping the post short. :_|

 

[Sidewinder]

Ahh, here it gets complicated!

"Officially" you need the impedance and reactance of the load.

Unofficially you "may" be able to ignore them!

They are related to the inductance and capacitance of the supply cable due to its design & manufacture.

It is assumed that a cable of this size will be carrying a commensurately high current which will generate its own magnetic fields and interact with the other cores and the insulation of the cable.

This may not be so.

Not quite as clear cut as it seems, hence why it's often ignored!

 

[Andy™]

1 mile of cable to replace..... that aint going to be cheap....

 

[batty]

somebody made a boo boo designing that circuit.

 

[Ian Speirs]

Not quite as clear cut as it seems, hence why it's often ignored!

Thanks for the quick reply, if ignored then what would i use to calc the volt drop?

 

[Sidewinder]

R mate ignore the x&z

 

[Ian Speirs]

[quote name='Andy

 

[Andy™]

could always just buy 110v gear instead....

 

[Ian Speirs]

somebody made a boo boo designing that circuit.

:slap

---------- Post Auto-Merged at 22:40 ---------- Previous post was made at 22:35 ----------

Not sure when i'm back on site, got a couple of church PIRs to do in the next couple of days. Will let you know if i find any more surprises or what they are gonna do.

 

[NozSpark]

somebody made a boo boo designing that circuit.

Do you recon it was designed like that, or if it's been altered? ; )

 

[kerching]

:slap ---------- Post Auto-Merged at 22:40 ---------- Previous post was made at 22:35 ----------

Not sure when i'm back on site, got a couple of church PIRs to do in the next couple of days. Will let you know if i find any more surprises or what they are gonna do.

Ah, Quintennial Reports...takes me back! Is it still the 'Wiring and Lighting of Churches' by Churchouse? Porcelain connectors, no bare Pyro touching Oak etc? or am I going back too far................. :coat

 

[Ian Speirs]

Ah, Quintennial Reports...takes me back! Is it still the 'Wiring and Lighting of Churches' by Churchouse? Porcelain connectors, no bare Pyro touching Oak etc? or am I going back too far................. :coat

Fused neutral boards are sill nice to see

Do you recon it was designed like that, or if it's been altered? ; )

Definatley add on's without checking properly.

 

[NozSpark]

Probably started out life as just a lighting supply

 

[Evans Electric]

Thats what I thought TBH

 

[Ian Speirs]

Couldn't find this fuse in the reg book.

It's the church main cut out fuse. Thought I'd take a photo of it after it just happened to fall out when I looked at the supply head.

 

[Andy™]

never seen one that shape before

 

[Ian Speirs]

Me neither. I recommended it be upgraded to 60 amp as its pulling 18 amps with all the lights on only.

 

[kerching]

Couldn't find this fuse in the reg book.It's the church main cut out fuse. Thought I'd take a photo of it after it just happened to fall out when I looked at the supply head.

Would a piece of 15mm copper pipe fit?.................. :coat

 

[wsoppitt]

need to reply to see pictures

 

[Ian Speirs]

need to reply to see pictures

Who, me?