Electrical Urban Myths

thecribber

Urban Myths in the Electrical Industry

Reading some of the posts on this forum I thought I would start this Thread to highlight and clarify some of the Urban Myths in the electrical industry.

Myth 1. Ring main circuits are not allowed
According to the wiring rules ring main circuits are, and always have been permissible. The confusion here has happened because for a period between the 4 edition of ET 101 being issued in late 2008 and the first ammendment in 2011, Ring main socket circuits In kitchens were not permissible This requirement was withdrawn in the 2011 number 1 amendment.

Myth 2. Neutrals are allowed / not allowed in light switches
The wiring rules do not refer to neutrals in light switches. It is not a problem if a light switch has a neutral and it is not a problem if it has none.

Myth 3. Sinks with plastic pipes don't need bonding
Rule 544.2.1 Requires that metal sinks be bonded. There is no reference in the rule to the type of pipe used and therefore the pipe used not revelent.

Myth 4. The required max height of light switched is measured to the fixing screws
Rule 530.6 requires that switches in domestic installations are fitted between 400mm and 1200mm. It is therefore clear that no part of the switch should be higher than 1200mm.

Myth 5. The height limit of 2.25m for distribution boards is measured to the top row of MCBs
Rule 530.5.3 states that the height is measured from the finished floor to the top surface of the board.

Myth 6. The rules are always changing
The current edition of the wiring rules came out in 2008, ten years ago. These rules have changed twice in that 10 years. Amendment No 1 in 2011 and amendment No 2 in 2016. I suspect that this myth came about because contractors in the past were not well informed. They only became aware of the amendments months or sometimes years after they were introduced thereby forming the impression that the rules changed a lot.

Myth 7. Inspectors are out to "Get You"
The role of an inspector in any industry is to ensure the rules are being followed. In the past inspectors who correctly carried out this role were portrayed as being out to "Get the Contractor" It is my opinion that this harsh portrayal of inspectors was created by parties who simply wanted to drive business in their direction. I have always found inspectors to be free with up to date information and very helpful.

Myth 8. A completion cert. is a piece of Paper to facilate ESB Networks
A completion cert. is a legal document confirming that the installation has been installed and Tested in accordance with the current wiring rules. It should never be supplied until the job is actually complete and tested

Myth 9. It is permissible to certify work carried out by others as long as it is tested
Electrical Contractors work a self certification system and are only allowed certify work which has been totally carried out by their company. There are two exceptions to this rule 1 A reconnection and 2 Customer has applied for and been granted a change of contractor

Myth 10. Reconnections need to comply with current rules
With the exception that earthing must comply with the current rules, installations for reconnection need only comply with the rules that applied when the installation was origionaly carried out. Reconnections need to be fully tested in accordance with Part 6 of the rules and a test record sheet produced. Any issues highlighted by the tests need to be corrected before the Completion Cert. is submitted. It is therefore impossible to accurately price a reconnection until it has been tested.

Myth 11. There is a limit to the number of light points allowed on a circuit
There is no reference to the number of light points allowed on a lighting circuit. Therefore the limit is simply determined by the MCB / Cable size and load.

Myth 12. Insulation resistance must be greater that >500 meg ohm
Rule 613.3 states clearly that the minimum value of Insulation Resistance required is 1 meg ohm (one meg ohm). This has doubled from the previous 3rd edition which only required .5 mohm (1/2 meg ohm). Cables and fittings installed outside and exposed to the elements will drastically reduce Insulation Resistance. In many installations it will prove impossible to achieve anything like 500 mohm. Installation resistance values of 4 to 10 meg ohms are completely normal in our damp envoirment. Remember 1 meg ohm is 1,000,000, ohms. (1 Million) and is a huge amount of resistance.

2011

^^ nice one

Tuco88

Nice thread, I have a bone to pick with the ring final circuits used in kitchens. It does not state in any text that you can use them (not in my one anyway) in the amendment 2011.

Are you going under the ol informative change sir?

Risteard81

Tuco88 wrote: »

Are you going under the ol informative change sir?

Being "Informative" as opposed to "Normative" means that it does not form part of the Wiring Rules. So it is true that there is no prohibition on ring final circuits in kitchens.

Tuco88

Risteard81 wrote: »

Being "Informative" as opposed to "Normative" means that it does not form part of the Wiring Rules. So it is true that there is no prohibition on ring final circuits in kitchens.

Yes thats why i was stating the 2011 change from what was normative to informative on that particular annex.

Still its the idea of a good practice to follow.

Risteard81

Tuco88 wrote: »

Risteard81 wrote: »

Being "Informative" as opposed to "Normative" means that it does not form part of the Wiring Rules. So it is true that there is no prohibition on ring final circuits in kitchens.

Yes thats why i was stating the 2011 change from what was normative to informative on that particular annex.

Still its the idea of a good practice to follow.

The objection many have to the 2 no. 20A radial circuits in a kitchen is that these socket circuits have the highest load in the house, and therefore the 20A instead of 32A circuits are more likely to suffer nuisance tripping.

2011

Risteard81 wrote: »

The objection many have to the 2 no. 20A radial circuits in a kitchen is that these socket circuits have the highest load in the house, and therefore the 20A instead of 32A circuits are more likely to suffer nuisance tripping.

I would think that nuisance tripping of a 20A MCB in a kitchen will only occur if the circuit is badly designed. B type MCB can deal with little surges without tripping. As can be seen here 40A will take at least 20 seconds to trip.

https://library.e.abb.com/public/114371fcc8e0456096db42d614bead67/2CDC400002D0201_view.pdf

Edit: Perhaps if a kitchen has a washing machine, tumbler dryer and dishwasher a 3rd radial should be considered. Personally I would prefer the MCB to trip if it is crossing the cure shown above.

Risteard81

2011 wrote: »

Risteard81 wrote: »

The objection many have to the 2 no. 20A radial circuits in a kitchen is that these socket circuits have the highest load in the house, and therefore the 20A instead of 32A circuits are more likely to suffer nuisance tripping.

I would think that nuisance tripping of a 20A MCB in a kitchen will only occur if the circuit is badly designed. B type MCB can deal with little surges without tripping. As can be seen here 40A will take at least 20 seconds to trip.

https://library.e.abb.com/public/114371fcc8e0456096db42d614bead67/2CDC400002D0201_view.pdf

Edit: Perhaps if a kitchen has a washing machine, tumbler dryer and dishwasher a 3rd radial should be considered. Personally I would prefer the MCB to trip if it is crossing the cure shown above.

I don't disagree, but it is what concerns some. In practice I suspect even a single 20A circuit would be unlikely to suffer much tripping (although not perhaps a great design). Ideally I like to see heavy loads (e.g. tumble dryer) on dedicated radials rather than the kitchen socket circuit(s). Of course that adds cost to the job though.

2011

Risteard81 wrote: »

Of course that adds cost to the job though.

Yes, but you get what you pay for

I think we need to try to steer people away from this “race to the bottom” attitude that some have. A house is the largest investment in most people’s lives, I feel they should spend a little extra for better wiring.

Risteard81

2011 wrote: »

Risteard81 wrote: »

Of course that adds cost to the job though.

Yes, but you get what you pay for

I think we need to try to steer people away from this “race to the bottom” attitude that some have. A house is the largest investment in most people’s lives, I feel they should spend a little extra for better wiring.

Absolutely. I completely agree. Unfortunately the punters don't always though!

thecribber

MYTH 13. B Type MCBs are for Domestic and C Type MCBs for Commerical

Rule 533.3.4. Deals with MCB Types or Curves and doesn't not differentiate between domestic and Commerical Installations. MCBs in all installations should initially have B Type characteristics. If it is expected that surge currents (normaly on startup) of 5 to 10 times the normal rated current it is permissible to use a C type MCB. If the surge current is 10 to 20 times the normal it is permissible to use a D type.
Therefore if the MCB is a 20 amp, the expected surge currents Must be 100 to 200 amps (5 times 20 and 10 times 20) to justify the use of a C Type. Many Commerical installations have all C Type MCBs. These Installations can not comply with the wiring rules as the majority of electrical circuits ((Particuarly socket circuits) do not have surge currents even approaching 100 to 200 amps.

2011

thecribber wrote: »

These Installations can not comply with the wiring rules as the majority of electrical circuits ((Particuarly socket circuits) do not have surge currents even approaching 100 to 200 amps.

Well it depends on the installation. For the average domestic installation (if there is such a thing) a B type is perfect, but for a workshop a C type may be more appropriate as welders, 110V transformers may be plugged in. This will mean that lower earth fault loop impedance values will be required to ensure that the disconnection times are not exceeded.

tweek84

One thing i did notice is myth 11 some inspectors will argue that point about no maximum number of lighting points. Annex 55a 4.2 a recommended maximum number of points: 10 (see definition of points)
Point: a termination of the fixed wiring intended for the connection of current using equipment
Yes it is in the socket section but lighting is wired in radial so it falls under the wiring of radial circuits so 10 points. I did have this argument with an inspector.

thecribber

Myth 14. Maximum Number of outlets on ring / radial circuits

A maximum of 10 outlets can be connected to each radial circuit. A twin socket and a single socket both count as one outlet. Each radial circuit should not supply more than two rooms. A landing / hall does not count as a room.

The number of outlets on a ring circuit is unlimited, but the ring circuit should not service an area greater than 100 square meters.

Cerco

thecribber wrote: »

Myth 14. Maximum Number of outlets on ring / radial circuits

A maximum of 10 outlets can be connected to each radial circuit. A twin socket and a single socket both count as one outlet. Each radial circuit should not supply more than two rooms. A landing / hall does not count as a room.

The number of outlets on a ring circuit is unlimited, but the ring circuit should not service an area greater than 100 square meters.

I think it should state ”either a single socket or a twin socket count as one outlet” .

Interesting.....100 sq. Metres for a single ring....that could be a whole house now days.

Great thread by the way!

They get less hot than incandescents certainly. But they come with heat sinks.



Diodes have a forward voltage drop.
Vf x I = Waste Heat.

Driving Circuits have switching components that devolve heat also.

GarIT

thecribber wrote: »

Myth 4. The required max height of light switched is measured to the fixing screws
Rule 530.6 requires that switches in domestic installations are fitted between 400mm and 1200mm. It is therefore clear that no part of the switch should be higher than 1200mm.

This is the most ridiculous thing I've read. Why can't I have light switches as high as I like.Can I not sign some document that states I will never allow a child or disabled person into my house and that if I become unable to reach the switch I understand the risks. I'm 1.85m, the light switches were around 1600mm which was ok but they would have been better higher but after a fire we had to have them moved to 1200mm to get the electricity turned back on.

Why should the person who uses the switches have to hurt their back bending down every time they want to turn on a light to be inclusive of someone who will never be allowed into the house?

2011

GarIT wrote: »

Can I not sign some document that states I will never allow a child or disabled person into my house and that if I become unable to reach the switch I understand the risks.

No. It’s a regulation just like the downstairs toilet in a new house must be wheelchair accessible.

JonnyM

GarIT wrote: »

This is the most ridiculous thing I've read. Why can't I have light switches as high as I like.Can I not sign some document that states I will never allow a child or disabled person into my house and that if I become unable to reach the switch I understand the risks. I'm 1.85m, the light switches were around 1600mm which was ok but they would have been better higher but after a fire we had to have them moved to 1200mm to get the electricity turned back on.

Why should the person who uses the switches have to hurt their back bending down every time they want to turn on a light to be inclusive of someone who will never be allowed into the house?

You may not always be living in that house.

Regulations only apply to those on the network.
The easiest thing to do would be get the mains disconnected, buy yerself a big battery, a coupla grand of gizmos, a generation system that can meet yer demand which will have to be hybrid and yer laughin'!

Oh wait there's an app for light switches these days..nevermind..

GarIT

2011 wrote: »

No. It’s a regulation just like the downstairs toilet in a new house must be wheelchair accessible.

Things like this really annoy me. Typically accessible things don't function as well for able bodied people and we all have to suffer to cater to a few. It would be cheaper overall if the government made anywhere wheelchair accessible on for free if a disabled person requested it than it would be making everything accessible by default.

JonnyM wrote: »

You may not always be living in that house.

I can change it back before I leave.

2011

GarIT wrote: »

I can change it back before I leave.

When you see the cost you may not agree, be able to afford it or may be dead (it happens). Then the taxpayer would have to pick up the tab.

red sean

2011 wrote: »

When you see the cost you may not agree, be able to afford it or may be dead (it happens). Then the taxpayer would have to pick up the tab.

As a matter of interest, why the taxpayer?

salmocab

I’m sorry but unless your exceptionally tall or have arms like a T. rex you don’t have to bend down to press a switch at 1200mm.

hufpc8w3adnk65

salmocab wrote: »

I’m sorry but unless your exceptionally tall or have arms like a T. rex you don’t have to bend down to press a switch at 1200mm.

If someone was that size they worked also need to duck going through doors, chabge they heights on shower heads.

@GarIT. Do you take issue with bending over to plug in and out sockets?

salmocab

MrMac84 wrote: »

If someone was that size they worked also need to duck going through doors, chabge they heights on shower heads.

Do you take issue with bending over to plug in and out sockets?

No not at all why?

hufpc8w3adnk65

salmocab wrote: »

No not at all why?

Sorry I ment that for the op and have edited my previous post

2011

red sean wrote: »

As a matter of interest, why the taxpayer?

For example:
Let's suppose that someone is suddenly becomes wheelchair bound (for whatever reason). There are government grants available to make this person's home more wheelchair friendly such as converting a bathroom and lowering light switches. Obviously this means that the taxpayer picks up the tab. However if the house already has some of these modifications in place already there is a cost saving.

GarIT

GarIT wrote: »

I can change it back before I leave.

Equally you could move the switch and move it back before you leave.
If one was inclined....

2011

Sir Liamalot wrote: »

Equally you could move the switch and move it back before you leave.
If one was inclined....

Or go Philips Hue and all light switch positions become irrelevant....

GarIT

salmocab wrote: »

I’m sorry but unless your exceptionally tall or have arms like a T. rex you don’t have to bend down to press a switch at 1200mm.

It depends on where you stand. If you don't walk right up for the switch and reach ata 45 degree angle you might have to bend/lean towards it a bit.

MrMac84 wrote: »

If someone was that size they worked also need to duck going through doors, chabge they heights on shower heads.

@GarIT. Do you take issue with bending over to plug in and out sockets?

I'm not that tall, last time I measured I was just over 6ft2 in Nike runners so I recon around 6ft1. I'd use light switches more often than plug sockets and would typically bend at the knees or waist for them. Something I do have a problem with is sinks, I havent found a sink I can reach without bending, I'd like most sinks to be 20-30cm higher but that makes them impractical for other people.

Sir Liamalot wrote: »

Equally you could move the switch and move it back before you leave.
If one was inclined....

As far as I know that would be illegal. I do know someone that would do it as a nixer but it's a hassle putting them in to the standards and then moving them and repaining and filling holes again.