SELV/Control wiring

[WaterSparky]

I was wondering if voltage drop applies to SELV etc voltages, situation in question like 24V AC & DC for control etc?
Surely not?

Along the same lines if 230V is used for control for example:

230V coming back from a panel and indicating when a item of equipment is running and indication lamps being lit in a control room or alike?
Does this come under voltage drop regulations?

Cheers

 

[Outspoken]

I was wondering if voltage drop applies to SELV etc voltages, situation in question like 24V AC & DC for control etc?
Surely not?

Along the same lines if 230V is used for control for example:

230V coming back from a panel and indicating when a item of equipment is running and indication lamps being lit in a control room or alike?
Does this come under voltage drop regulations?

Cheers

I'll give you a clue...IT'S CALLED VOLT DROP​, it is not not 230V drop!!

 

[WaterSparky]

Sorry I'm only an apprentice, it was only a question. So I don't know what I did to cause that reply?

 

[stuartcourt]

nothing we just get some stupid questions but fine from an apprentice think you got your answer though

 

[ferg]

I can't remember where I saw it, but someone on here has a sig

"once you have enough knowledge to satisfy the old boys you're too old and knackered to use it"

In my opinion there is no such thing as a stupid question, just a stupid answer

As an apprentice I got used to hearing.."what the .... do they teach you at college!!!"

If you start your questions with I'm an apprentice you might get a bit more slack

 

[v.elec]

I'll give you a clue...IT'S CALLED VOLT DROP​, it is not not 230V drop!!

Unnecessary.

 

[plugsandsparks]

I used to have an escort rally car and needed really bright lights. When i measured the volts at the lamps i was getting 10.8 instead of 13V. I re-wired the lighting taking a feed directly off the alternator, through relays and re-wired direct ground cables to the chassis, all in the name of reducing volt drop and that was only 12V DC, so yes i matters alot.
cheers

 

[WaterSparky]

Thank you I'll just put my sig as Apprentice haha.

I was just thinking with with 24V DC you couldn't really apply volt drop (obviously you could but it's slightly different) as it's not really like mains voltage and is a part of a control circuit for starting a pump or on emergency stop. Struggling for words here really.

 

[KAS1]

Put it this way 24v on a 100mt cable run controlling a relay or control valve I think you'd have to consider volt drop

 

[WaterSparky]

Think I worded this wrong from the start. My understanding WASNT that some how magically 24V or selv was immune to voltage drop. I just meant would the selv/control part of an installation fail the electrical installation certificate? Even if the control part was over the allowed values, just made me think that I was at work we fault finding a motor starter, and the 24V coil was still pulling in at around 19V.

Cheers for the replies though guys

 

[Darkwood]

Think I worded this wrong from the start. My understanding WASNT that some how magically 24V or selv was immune to voltage drop. I just meant would the selv/control part of an installation fail the electrical installation certificate? Even if the control part was over the allowed values, just made me think that I was at work we fault finding a motor starter, and the 24V coil was still pulling in at around 19V.

Cheers for the replies though guys

Dont get confused here - control circuits and systems are a seperate entity and dont fall under the BS 7671, if you are issuing a cert' then you should issue one relevant to the control system ... you Installation Cert ends at the supply to the control unit.

A knowledge of control circuit regulations, protection and operation as well as an understanding of risk assessment are needed before issuing any form of cert' for a control system.

Having said all this their are times when you can cover the install of a control system under a standard Condition Report -like say a simple start / stop all in one contactor operating a pump etc.... as long as you have an understanding of its workings ....i.e. Correct overloads, correct control voltages for the situation etc etc...

I personally would issue a separate inspection report on the control system which is more suited to the set-up and only include the supply to the control system on a Electrical Condition Report.

 

[johnboy6083]

"In the absence of all other considerations, under normal service conditions the voltage at the terminals of any fixed current using equipment shall be greater than the lower limit corresponding to the product standard relevant to that equipment."
525.1

This is the realm of BS7671, but I believe it's good enough to apply anywhere.
In some circumstances, volt drop has to be constrained to very tight limits, in others it can and will vary greatly.
For control systems, Read the instructions of the equipment, it will specify voltage limits.

 

[WaterSparky]

Thanks guys, I this a bigger thing at work where we've been told to do more certificates and I was talking with the blokes like how far do we go? Ya know down to the instrument/ control circuit etc! Thanks for the help!

 

[Outspoken]

Sorry I'm only an apprentice, it was only a question. So I don't know what I did to cause that reply?

WaterSparky, had you stated you were still an apprentice when you began your post then you would have got a slightly less terse response, but my response should have been taken as a definitive statement and not a dig at you per se. If it caused you offence I apologise as that was not the intent...Look below for intent

Unnecessary.

And your post is utterly pointless and unhelpful, so instead of being a troll, why did you not answer the poor lad definitively, or are you showing a gap in your understanding...?