Reducing voltage problem

[ajelectrical]

Has anyone had this problem before.?

I had to test a ring circuit in a cafe as the voltage is reducing when appliances are switched on causing the mains voltage to drop as low as 187v ac. The voltage is 236v ac before appliances are switched on. This is causing some items not to work. ie lighting, radio microwave.

The cables to the appliances show no signs of damage.

Ring circuit continuity is fine and the circuits meggars clear.

It is a TT supply to the property and the whole board is protected by a 30ma RCD and a 32amp MCB to the ring circuit.

Any advice please if this could be a problem with the overhead supply cable or any of the appliances.

Many Thanks, Alan

 

[steptoe]

have you calc'd the volt drop?

have you confirmed the connections at the DB ?

if so then a dno joint by the sounds of it, or a meter monkey with a limp wrist......

 

[SPECIAL LOCATION]

what are your r1, r2 & rn

and what are your R1+R2 for the suspect circuit.....?

Appendix 2 page 242 of the old Red book suggests that incoming voltage is ok if between

216.2v - 253.0v

Guinness

 

[Evans Electric]

I would guess that the network cables in that area need upgrading , so when you apply a load at your job the voltage drops .

If you did it at midnight with other properties on reduced load it may not happen.

It happened in an area of this city when I was an apprentice , I didn't grasp at the time what was causing it . It was always early evening with everyone home from work , cooking and being winter , electric heating on. I remember the fire elements reducing to a cherry red colour and hardly any heat radiating from them, the socket warming up and the TV picture getting smaller. Then by about 8.30 pm it would return to normal as cooking ceased and the voltage improved.

Whole area was dug up and new supply cables laid .

 

[ajelectrical]

Thanks for replies.

I will get cafe owners to contact their supplier to have supply cable and meter checked.

Alan

---------- Post Auto-Merged at 00:57 ---------- Previous post was made at 00:51 ----------

Hi

The r1 = 0.48 rn = 0.47 and r2 = 0.72. r1+r2 = 0.30

Thanks, Alan

 

[ProDave]

You have not said WHERE you measured the voltage. That is crucial.

What you need to measure is the incoming voltage right at the input terminals to the main switch. If that's dropping that much then it's a DNO problem for them to sort out.

 

[Evans Electric]

He said " Mains voltage " Dave, which I took to mean the incoming . I think it must be their problem unless the place is wired in doorbell cable .

 

[Andy™]

if the voltage drops at intake, then its a loose connection on DNO side. if intake stays OK, but circuit drops, then somewhere on the installation

also, if its external, then other circuits will also be effected and have a lower voltage

 

[wozz]

Sounds like a loose DNO joint, or a neutral terminal in the first DB/ switchfuse thats common for all circuits. You may also find your L-N loop is high. I have a customer with a similar problem but getting the DNO to do anything about it has proved to be fruitless so far!

 

[Sidewinder]

wozz,

If you have an idea that the bad joint is in the property then tell them you can smell burning!

 

[wozz]

Sides, this particular property voltage problem is caused by being at the end of a very long run, L-N loop is about 0.45 when I checked, DNO do not want to upgrade due to HV is miles away! Even though the engineers openly admit it needs a micro sub for the property (2x100A supplies). Its that bad switch start florries regularly drop out when somethings turned on.

To be fair when Ive had loose neutrals our DNO UKPN and been pretty good. The OP does sound like a loose neutral but could be in a really poor area network wise!?

 

[Evans Electric]

Are the DNOs not obliged to provide a supply within certain parameters . Someone will know ,save me looking :Blushing

 

[Sidewinder]

They are ESQCR!

You could get the tenant to complain of flicker, they have to take this very seriously due to the possibility of inducing epileptic fits!

 

[ajelectrical]

Thanks for replies guys.

The voltage was being measured at the intake.

Alan

 

[Sidewinder]

Alan,

Sounds like a DNO issue then!

Try the L-N & L-E fault loop readings & check the N-E resistance.

You'll hav to work in a safe manner doing this obviously.

Also check your Ze.

What is the supply type?

Are there any other nearby houses affected?

How is the supply delivered to the premises, OH?