Workshop wiring

[robin colemanParticipant @robincoleman77853]

I am having some electrics put in the workshop how many amp does a small pillars drill use and a small watchmakers lathe they all runn off a 13 amp plug but I doubt if they use a full 13a

[Craig BrownParticipant @craigbrown60096]

Without knowing the rating of the motors fitted to each its hard to say for sure but a watchmakers lathe and pillar drill, sized for similar work, I think it would be safe to say they will be below 3A each. I assume both won’t be used simultaneously so that’s also a consideration

[Peter Cook 6Participant @petercook6]

Pillar drill will be <500W so < 2 amps. Watchmakers lathe will be <1 Amp unless you have fitted an enormous motor!

My workshop (LED Lighting, SX1LP mill with DRO, Taig lathe, couple of watchmakers lathes, filing machine, belt grinder, dremmel, bench grinder, etc, etc, etc) runs off a 13amp fused spur from the house with no problems. You only use one machine at a time typically. Most power hungry device I have is a 2Kw oil filled heater.

[robin colemanParticipant @robincoleman77853]

Ok thank you I am going to separate the sockets lights etc on a consumer unit it runs from a fused spur to the outside plug for the spar but is never on permantly the only device which may draw power is the arc welder which i occasionally use in the workshop if desperate but I mainly run that off a house socket.

[noel shelleyParticipant @noelshelley55608]

I would suggest that if being done professionally that you consider 16 amps as the minimum from the house or a ring main and lighting circuit. That will give you plenty. The items you have mentioned will be about 3 amps running, but starting or any heating or a small welder will soon add up. Noel.

AH SO, now you mention a welder, this may well exceed 16A ! You should have told us this first ! I would talk to the electrician you intend to sign it off as he will know better than some of us.

[robin colemanParticipant @robincoleman77853]

I have a background in electro mechanical engineering a d electronics and made my first tv from parts when I was 11 so a bit of wiring should be ok I will just get an electrician to sign it off.

[Mark P.Participant @markp]

When I had my bungalow rewired I had a dedicated 40A supply taken to my workshop.

Regards Mark P.

[HollowpointParticipant @hollowpoint]

There’s some wild estimates in here.

Motors can draw plenty of amps on startup and no one has considered amps drawn under load.

Your gonna need a minimum of 16a for a small workshop imo.

[Howard LewisParticipant @howardlewis46836]

Presumably, the workshop will have a circuit for lighting, and another, Ring main for to feed the sockets.

The lighting circuit will probably be 5 Amp capacity (Particularly with LEDs, which do not have the instantaneous start up surge of fluorescents)

The ring main, in UK will supply a number of 13 Amp sockets, so should be capable of carrying, 16 Amps, to allow for start up surges from motors. The ring main will allow any socket to be fed from both sides, so the full 13 Amps should be available.

If in doubt, consult, or employ, a professional electrician.

If you don’t know what you are doing, and get it wrong, you could have a fire, or finish up dead!

Better be safe than sorry

Howard

[Trevor Drabble 1Participant @trevordrabble1]

Since any qualified electrician will need to ensure compliance with both BS 7671 and also Part P of the Building Regulations before he signs it off , would suggest you consult him first before you go any further.

[Robert Atkinson 2Participant @robertatkinson2]

With the exception of the welder a 13A spur would be adequate for you workshop. As mentioned a hetar is likely to be the worst offender. A good solution would be a dedicated radial from the main consumer unit rated at 16A feeding a small consumer unit in the workshop with a 10 or 16A RCCBO feeding 13A sockets on a ring and separate 5A RCCBO feeding the lighting circuit.

Robert.

[OldironParticipant @oldiron]

I would go for at least a 30/40 amp supply for a workshop. You will always add more and more items to the supply. ie radio, lights, compressor, fan, welder, drill press, small lathe, small mill, Vacuum cleaner etc etc.  Then plug in the lawnmower, leaf blower ad infinitum.

[duncan webster 1Participant @duncanwebster1]

I have a 30A spur from the main dist board to a secondary one in the workshop. Never managed to overload it

 

[Oldiron]

On Oldiron Said:

I would go for at least a 30/40 amp supply for a workshop. You will always add more and more items to the supply. ie radio, lights, compressor, fan, welder, drill press, small lathe, small mill, Vacuum cleaner etc etc.  Then plug in the lawnmower, leaf blower ad infinitum.

When do you use the machine tools, lawnmower (you have a lawn in you workshop 😉  ) and leaf blower all at the same time?

I’d be lucky to get 30 Amps for the workshop. The feed to the house is only 60 Amps and that has to supply the heat pumps, cooker, kettle washing machine etc.

I have a 13A switched spur of a ring main. Fine or the SX2LP ML7 with VFD and nanthing I heed to run at the same time.

[noel shelleyParticipant @noelshelley55608]

A pickhill/ oxford oil cooled 180A welder WILL need 30A and this is not a big machine the 110A WILL blow 13A fuses, been there ! A modern 170A inverter welder will just about run on a 13A plug – solong as you don’t run it full cap.

So 4mmsqu ( or more ) and 32A is your best bet as you have a welder. Even then you may have issues with the inrush current. Noel.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, well I have a 15mm sq. cable from a 40A trip, to a junction box inside the house, which then goes through the wall with a 10mm sq. armoured cable to my garage to a consumer unit in the garage, total length of cable is about 15 to 16 m. My welder has a 30A inrush, and won’t work very well on anything less. I’ve had no problems with the set-up, and yes the whole electrics have had a full test, but I think it is due for a new test this year.

Regards Nick.

[Nigel Graham 2Participant @nigelgraham2]

My workshop seems to have no more than a 13A spur from its own rcd on the main distribution board; without problems, despite it at times feeding the Harrison lathe or Myford VMC mill with 3ph conversions, plus the two ceiling l.e.d. strip lamps off the same spur. This wiring was installed by a previous owner.

I am course only running one machine at once.

I don’t know what either welder draws but they are low-power appliances run from a 13A socket normally. I do not use them often and then outdoors (so no lights or anything else on) but may be better plugging them into a ring-main socket in the kitchen.

Nevertheless I think it would be wise for me to follow some of the advice here and have the supply renewed and up-rated.

 

(To be honest I am not entirely happy about the whole house wiring though. PVC cables slung across a void below the middle room floor, with no clipping-up for the full eight feet or so span, does not look good practice. There are a couple of plastic barrier type water-pipes similarly dangling in the gloom.)

[Chris CrewParticipant @chriscrew66644]

I think it depends where your workshop is located. Somebody please correct me if I am wrong but my understanding is that ‘Part P’ regulations only apply to the main residence. If your workshop is located remote from the house you don’t have to have anything certified by a ‘qualified person’ that you do in there, although it may be prudent to have this done if you have any doubt in your own abilities. My workshop is 15 yards from the house supply and is fed by a 3-core 6mm buried armoured cable from the domestic consumer unit via a 32amp MCB. This terminates in a workshop consumer unit which feeds two rings of 6 double 13amp sockets from 16amp MCBs and a 5amp MCB lighting circuit. The wiring is all contained in trunking and conduit, all properly installed by myself with nothing ‘bodged up’ with insulation tape or strip connectors. The feed from the house was connected by myself before Part P applied – no really, it was!

[EmgeeParticipant @emgee]

Chris

You don’t mention any type of out of balance current operated circuit breaker in your supply line, you may of course have such a device fitted in the power supply to the house consumer unit.
The workshop supply should be via a double pole isolation switch at the point of supply for isolation purposes.
You are exporting the cpc from the house system but this may not comply with current regulations.

I would suggest fitting a 30ma operating current RCCB incomer to the workshop consumer unit for your personal safety.

Emgee

[Chris Crew]

On Chris Crew Said:

I think it depends where your workshop is located. Somebody please correct me if I am wrong but my understanding is that ‘Part P’ regulations only apply to the main residence. If your workshop is located remote from the house you don’t have to have anything certified by a ‘qualified person’ that you do in there, although it may be prudent to have this done if you have any doubt in your own abilities. My workshop is 15 yards from the house supply and is fed by a 3-core 6mm buried armoured cable from the domestic consumer unit via a 32amp MCB. This terminates in a workshop consumer unit which feeds two rings of 6 double 13amp sockets from 16amp MCBs and a 5amp MCB lighting circuit. The wiring is all contained in trunking and conduit, all properly installed by myself with nothing ‘bodged up’ with insulation tape or strip connectors. The feed from the house was connected by myself before Part P applied – no really, it was!

Part P applies.
From https://assets.publishing.service.gov.uk/media/5a802da7ed915d74e622ceed/BR_PDF_AD_P_2013.pdf

“The requirements of this part apply only to electrical
installations that are intended to operate at low or installations that are intended to operate at low or
extra-low voltage and are:
extra-low voltage
and are:
(a) in or attached to a dwelling;(a) in or attached to a dwelling;
(b) in the common parts of a building serving one or(b) in the common parts of a building serving one or
more dwellings, but excluding power supplies to lifts;more dwellings, but excluding power supplies to lifts;
(c) in a building that receives its electricity from a source(c) in a building that receives its electricity from a source
located within or shared with a dwelling; or located within or shared with a dwelling; or
(d) in a garden or in or on land associated with a building(d) in a garden or in or on land associated with a building
where the electricity is from a source located within orwhere the electricity is from a source located within or
shared with a dwelling.shared with a dwelling.”

Clauses c and d clearly apply to a shed or outside workshop.

In fact because it is “outside” the connection to to your workshop is notifiable work and must be reported.

Robert.

[noel shelleyParticipant @noelshelley55608]

For larger motors eg 3Hp ( more so old ones ), transformer welders and 110V transformers all have high inrush current and need special consideration if nuisance tripping of breakers is to be avoided. Noel.

[SillyOldDufferModerator @sillyoldduffer]

Well, in the interests of pragmatic solutions.

• For a typical small workshop, obeying Nigel’s rule, only run one machine at time, then a 13A spur covers most cases.  Mostly, not always.
• The amateur electrician has to be very careful to stay small, and not overload the spur by adding lights, electric heaters, several machines, or anything greedy like a welder.  Do the maths.    Ignorance is not bliss!
• Amateur electrician also has to be honest about his actual rather than perceived competences!  Overconfidence based on limited experience can easily result in a bodged fire and safety hazard.   Building a TV set in 1970 is a good start, but the experience does not make one a qualified electrician up to date with current regulations and best practice.  Beware.
• Robert identifies the rules applying to a permanent installation.  The rules don’t apply to temporary arrangements.
  • A shed wired with an feed led across the garden to a consumer unit and permanent sockets, a fixed installation, is notifiable.  The advantage is it will be safe, reliable, and correctly sized.
  • The same shed wired by an extension lead, to which further extensions are plugged in, isn’t an installation, so the owner can do what he likes.  Less safe, less reliable, and might be incorrectly sized causing voltage drop, overheating and blown fuses etc.   Approach with caution!
  • My workshop is a mix:  it’s fed by a regulation compliant double socket on a ring, wires inside conduit.  The double socket is metal for strength, not plastic, because it might be bashed.   The lighting is on a separate circuit, also regulation compliant.   But, the several machines I own are run from switched 4-way extension leads, each individually fused.   As these aren’t notifiable, it’s my job to make sure the arrangement is safe and not overloaded.   For example, I’ve arranged it such that my mill and lathe cannot both be switched on at the same time:  they both have a 13A plug, and there’s only one 13A socket in reach.   On the bench 10 sockets are available for light loads, but they are all temporary extensions.

UK electrical regulations are a response to a long catalogue of accidents caused by badly installed and operated electrics, not Health and Safety gone mad!   When judging the risks “common sense” and individual experience are low value compared with the statistics.  They show fires are more common than electrocutions, killing people by smoke inhalation rather than zapping them.   As a badly done permanent installation in a workshop risks burning the house down, the rules apply, and wise owners should do a proper job. But the risk can also managed by unplugging an extension lead.   OK unless you is forgetful or irresponsible.

In the UK, bad DIY electrical work done by home-owners isn’t policed.   If an electrician finds a house full of non-compliant foolishness, he’s unlikely to shut it down.    The pain comes if the house burns down and the insurer refuses to pay.  And when it’s time to sell the house, purchasers are likely to have the electrics surveyed, and a non-compliant installation takes many thousands off the value.  Change of ownership might cause the supplier to install a new meter, when he becomes aware the wiring is unsafe and refuses to provide. No problem if the clown who messed up is deceased, but a serious worry if he’s selling up to move into a bungalow, or care home, or wants to go on a world cruise!

Somewhere on youtube there’s an interesting video of an electrician exploring a home heavily rewired by an ex-works electrician.  He finds rats nest that ignores all the guidelines.   Turns out the ex-works “electrician” was an installer, working   to plans prepared by a qualified supervisor, not fully qualified himself.   His misplaced confidence came from knowing the practical side, but he didn’t understand the rules, or why they mattered, or that he’d done anything wrong.   Until it was explained…

I sometimes bruise egos by pointing out that our experience and skills may not be up to the job!   No offence intended, the reality is that none of us are perfect.  Whilst confidence is a virtue, over-confidence is a sin.   Avoiding problems by having a little think is surely better than crashing on regardless.   Ask is this dumb, different or dangerous?  Then proceed.

Dave

[Robert Atkinson 2Participant @robertatkinson2]

Unfortunatly the other side of the coin is that a lot of “registered” electricians have litle understanding of the fundamentals. Many also consider BS7671 as legislation, which it it not (there is a slight oddity in the private landlord legislation but lets not go there) and must be followed blindly. This is not the case BS 7671 is a standard that if followed provides an accepted means of compliance with the legislation.
Even worse a “Part P” contracting firm may have a single “Registered Competent Person” “overseeing dozens of technicians of variable competence. They don’t have to phyically check any of the work. It’s down to the integrity of individuals. As we all know for some people making a profit is more important…

My recent experience with “electricians” has been less than satisfactory to put it nicely.

[noel shelleyParticipant @noelshelley55608]

Spot on Robert, I to have signed off electrics that are far from right. Some of the worst cowboys are the ones that have done the course and got the bit of paper. I may not be upto date on the latest regs but I know what is safe and have the gear to do the tests. Noel.

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