electric shower tripping

[Davisonp]

One other test is to turn off all other circuits to ensure the shower trips the RCD on it’s own, not a combined leakage issue.

 

[neilyboy]

Wonder if the OP is charging for this?

So its a recent install, the customer bought the kit, the installer isn't returning calls, the OCPD may be too low, we don't know if the RCD or MCB are tripping.

We do know the person fault finding doesn't have the appropriate kit.

Has it ever worked?

Did the installer provide a cert?

Wonderful!

1.no, i have a pension i dont need to charge
2.ok i should have taken notice of this
3.ministry of bleeding obvious....new install tripping...course its never worked
4.of course not he's disappeared with his money
As a long time ex sparky i enjoy reading most of these threads to try and keep up but some of you guys and your replys just fill me with dismay with the sarkiness and all round General contempt you treat genuine querys. unless i

 

[Octopus]

^^ you read this forum regularly yet start a thread full of holes.... Are you real?

Your "friend" needs to report this chancer to trading standards, the employ a reputable spark with current practice, skills, expertise, and test kit

 

[neilyboy]

^^ you read this forum regularly yet start a thread full of holes.... Are you real?

Your "friend" needs to report this chancer to trading standards, the employ a reputable spark with current practice, skills, expertise, and test kit

Yes i am real
And what holes
,why do you feel the need to put friend in inverted commas

 

[Specialist]

@neilyboy: In your original post you said that you were looking for a fault on a 9.8 kW shower, that was fed via a 40a MCB & 63a rcd which trips when the shower is turned on.
You have no test equipment & decided to fault find by first bypassing the switch, then connecting the shower to the incoming mains supply. Neither of which are safe or recognised fault finding techniques, then come here & ask for help.
You were given the most probable causes by telectrix & others in the first few replies you got. The people who've taken the time to reply to you, do this job day in / out & get annoyed when people use dangerous practices to try to find a fault. So yes you will get sarcastic & contemptuous replies.
My best suggestion to you now would be to tell your friend to contact a proper electrician in, who has the correct knowledge & equipment to find and clear the fault safely.

 

[davesparks]

As an ex electrician you should surely appreciate that proper test equipment is required to find a fault such as this, and also understand that just because the shower appears to work when the RCD is removed it doesn't mean it is working correctly or safely?

 

[The Ghost]

9.8kw appliance and its 40.833333333a.

Funny I get 43a

 

[Specialist]

Funny I get 43a

Think the OP did his calc based on 240v.

 

[Wilko]

Funny I get 43a

Often manufacturers quote power used at 240V for their rated power but it should be on their instructions

 

[davesparks]

Funny I get 43a

Then presumably you've calculate s it using the wrong voltage. The power rating system of appliances are still given at 240V almost universally, many will have their 230V power rating given additionally in smaller writing.

A resistive load of 9.8kW at 240V will only be around 9kW at 230V

 

[The Ghost]

From a design perspective @davesparks , while I appreciate technically you are correct, using 230v as the nominal voltage in calculations gives you a safer margin of error in cable selection. This is also specified at pg 316 BS7671. Now before you say well if you do that by the time you get to 30v you would end up with 9800/say, 30v = 326 amps...Design parameters dont go down from 230v. So who of you calculate say PFC with anything but 230xCmin/Zs or ccc with anything but xw/230? And I do understand if you take the resistance of the element and R =V/I and manufacturers instructions and specifications, but still if I was designing the circuit and deciding on the cable that is the way I have been taught. And I have had this "discussion" before and taken it back and written the various viewpoints calculations up on the whiteboard from both viewpoints and the tutor in question still insisted that all design calculations assume harmonised voltage, which at the end of the day only makes things safer. Let fly the dogs of war!

 

[Rpa07]

From a design perspective @davesparks , while I appreciate technically you are correct, using 230v as the nominal voltage in calculations gives you a safer margin of error in cable selection. This is also specified at pg 316 BS7671. Now before you say well if you do that by the time you get to 30v you would end up with 9800/say, 30v = 326 amps...Design parameters dont go down from 230v. So who of you calculate say PFC with anything but 230xCmin/Zs or ccc with anything but xw/230? And I do understand if you take the resistance of the element and R =V/I and manufacturers instructions and specifications, but still if I was designing the circuit and deciding on the cable that is the way I have been taught. And I have had this "discussion" before and taken it back and written the various viewpoints calculations from both viewpoints and the tutor in question still insisted that all design calculations assume harmonised voltage, which at the end of the day only makes things safer. Let fly the dogs of war!

I'm sure that it's easier just to say 'up yours' - but since you went to all the trouble, good post @Vortigern

 

[Octopus]

Yes i am real
And what holes ,why do you feel the need to put friend in inverted commas

Hum..

What holes - clear admission of insufficient test kit, random approach to testing, didn't confirm in initial post it had never worked

"friend" - If I had £1 for everybody that initially claimed to be doing this for a friend on here I could probably have a decent holiday...

Just saying.

 

[The Ghost]

take a load of 10kW @ 240V for example.

P=I V so I = P/V = 10,000/240 = 41.667A

from that using ohm's law, R = V/I = 5.76 ohms

now assume that V =230V

I =V/R, so I= 230/5.76 = 39.93A

so @ 230V P = VI = 9.184kW.
This is what Pete999 or was it telectrix posted in support of the previous "discussion" re counter argument to using 230v which is undeniable. I just post this to save you having to re-post it. I get it.

 

[The Ghost]

say 'up yours'

Well it does say to post polite and professional though

 

[davesparks]

From a design perspective @davesparks , while I appreciate technically you are correct, using 230v as the nominal voltage in calculations gives you a safer margin of error in cable selection. This is also specified at pg 316 BS7671. Now before you say well if you do that by the time you get to 30v you would end up with 9800/say, 30v = 326 amps...Design parameters dont go down from 230v. So who of you calculate say PFC with anything but 230xCmin/Zs or ccc with anything but xw/230? And I do understand if you take the resistance of the element and R =V/I and manufacturers instructions and specifications, but still if I was designing the circuit and deciding on the cable that is the way I have been taught. And I have had this "discussion" before and taken it back and written the various viewpoints calculations up on the whiteboard from both viewpoints and the tutor in question still insisted that all design calculations assume harmonised voltage, which at the end of the day only makes things safer. Let fly the dogs of war!

There is no need to add artificial margins of error in to these calculations, the cable ratings we use have quite enough margin and headroom built in to them already.

If you have a piece of equipment where the data plate quotes power rating A at 240V and power rating B at 230V then it is just plain wrong to calculate based on rating A at 230V.
You can't say that design parameters don't go down below 230 therefore we can happily ignore the facts.
The calculations for Zs that you mention are not relevant to this point, they have to be based on the nominal value because the mains voltage is not fixed at a specific value, the power ratings of an appliance are fixed at a specific value at a specific voltage.

The opinion of one tutor is not going to change pure scientific fact.

I just don't understand how people can be so blind to the laws of physics

 

[The Ghost]

Well as I said I can agree with your viewpoint without slur or demur, however there is it seems another viewpoint that does ignore your science and goes for a margin that obviously you dis-agree with. If you are truly based on scientific fact you will of course be aware that very often we get (or at least I do) 247/9 v. What do you do with that scientifically measured fact in design? And what if in the future tappings are changed to 230v? Do you inbuild future possibilities like someone adding a couple of sockets and a cooker to a ring for instance? Please bear in mind I am acting devils advocate as this subject bugs me and it is meant in a spirit of enquiry and healthy discussion.

 

[westward10]

And the band played on

 

[GlenTavener]

I dont have a megger, I have a fluke, Installation practices of 40 odd years ago are still practiced today,its the way they are installed ie bad workmanship that cause the problems,wiring systems have not changed since I was on the tools but certain regs have,earthing,testing,circuit discrimination I could go on but ultimately most of it is down to bad practice.
I would have had my a**e booted from my journeyman for some of the installations I have seen

Bad workmanship has not changed it existed 40 years ago as it does today but installation practices have changed considerably. Now there are much refined methods of fault tracing brought into being because the old ways were not sufficiently reliable. To attempt such work now it is advisable to first become fully aware of all the parameters involved. I trained in the early 60s but would in no way say that the "things" are still the same things, the basic circuit principle is but the method of safe control has been much enhanced. We no longer look round for a metal water pipe to wrap an earth wire around.

 

[davesparks]

Well as I said I can agree with your viewpoint without slur or demur, however there is it seems another viewpoint that does ignore your science and goes for a margin that obviously you dis-agree with. If you are truly based on scientific fact you will of course be aware that very often we get (or at least I do) 247/9 v. What do you do with that scientifically measured fact in design? And what if in the future tappings are changed to 230v? Do you inbuild future possibilities like someone adding a couple of sockets and a cooker to a ring for instance? Please bear in mind I am acting devils advocate as this subject bugs me and it is meant in a spirit of enquiry and healthy discussion.

It's not my science, it doesn't belong to me, it's just the laws of physics. You might as well be disagreeing with gravity. I disagree with adding an extra margin on top of the margins that have already been allowed in the system, it just leads to a waste of materials. It's not just in electrics that I have this debate, it's in other areas I work too.

I am aware of the fact that substations in the U.K. Output at 250V/433V, even the brand new ones being built today are the same. they don't normally have any option to change this at that level, the tap changers are normally only fitted at the 11kV level, so to actually drop to 230V they would have to lower the 11kV network. There are many problem with doing this so I think it is fairly safe to say that it isn't going to be happening any time soon.

The ring circuit is by its nature already designed with the ability to have additional sockets added, but is again irrelevant to the question.

You seem to be confusing the original point, which is that a fixed load rated at 240V you should calculate at 240V, with other areas where you don't have fixed values to work with and consequently would use the nominal value.

There are many areas in design guides, BS7671 and the various guidance notes where we are told that in the absence of better information we should use the nominal values.