Electrical Assignment Questions Please Help

[Steph1321]

Hi I am currently studying a degree in hospitality management and for one of the modules I have to supply answers on some electrical questions I have struggled to find information on some of these questions and I was hoping someone would be able to help?

The questions I have are:

1. What sort of consumer unit/fuse box does your establishment have?
· Is it a ceramic fuse block with different capacity fuse wire fitted?
· Is it a fuse box with large fuse cartridges instead of fuse wire?
· An MCB (miniature circuit breaker) style of consumer unit?
What are the advantages and disadvantages of each type of consumer unit?
I havent been able to find much at all on the differnent types of unit.

1. There should also be an overall protection device that will trip all the power in case of a severe problem, this used to be an Earth Trip switch, but in modern consumer units it is an RCD.



· How does an RCD work?
· Why might an RCD trip out?
· Why is an RCD safer than a fuse?



2. What should you do if an RCD covering the kitchen keeps tripping out on a busy Saturday night?


2. What colour should the outside sheathing of a PVC ring main cable be under new regulations?

3. Why does a TV have 3 amp cartridge fuses in its plug but an electric fan heater have a 13 amp fuse?


4. What would happen if you got them the wrong way round?

Im really sorry there are so many but any help would be great!!!

 

[Spudnik]

Hi and welcome

One of the lads will help you out im sure.

 

[telectrix]

same exact questions asked on a thread last week.

 

[Silly Sausage]

Greetings fella!

What type of establishment are you talking about?
Domestic, Commercial or Industrial?

 

[Silly Sausage]

same exact questions asked on a thread last week.

Must be on the same course.

 

[Steph1321]

Commercial it has to be based on my place of employment which is a holiday park. thanks

 

[ringer]

...

1. What sort of consumer unit/fuse box does your establishment have?
· Is it a ceramic fuse block with different capacity fuse wire fitted?
· Is it a fuse box with large fuse cartridges instead of fuse wire?
· An MCB (miniature circuit breaker) style of consumer unit?

What are the advantages and disadvantages of each type of consumer unit?

Bit of a tricky one to answer. The first two types are for older electrical installations. They are ok, they will provide overcurrent protection, and were suitable according to the regulations at the time they were installed. The regulations have now changed and this type of overcurrent protection is no longer allowed in new installations. Because they complied at the time of installation, and because more recent regulations are not retrospective, they can continue to be in service as long as they are in a satisfactory condition without deterioration. A qualified electrician will be able to assess whether the consumer unit (and the installation) remains in a serviceable state. He will do this by providing an Electrical Installation Condition Report (EICR), previously known as a Periodic Inspection Report (PIR)
The third type, is the preferred 'modern' way of providing overcurrent protection. This is because MCBs are more robust (they can withstand higher fault currents and still operate satisfactorily) and they are a simple switch, therefore easier to reset. Or, indeed, to isolate a circuit if required.

1. There should also be an overall protection device that will trip all the power in case of a severe problem, this used to be an Earth Trip switch, but in modern consumer units it is an RCD.

· How does an RCD work?
It checks for an imbalance between the line current (current in via the brown or red wire) and the neutral current (current out via the blue or black wire). If it detects an imbalance, it shuts off the power by isolating both poles (the line and the neutral)
· Why might an RCD trip out?
a) too much earth leakage from appliances in use
b) a fault on the circuit
c) a fault in an appliance (possibly electrocuting someone)
· Why is an RCD safer than a fuse?
it trips much faster and can detect different sorts of faults. However - an RCD should never be used on its own. It should always be used in combination with a fuse. A fuse provides overcurrent protection. An RCD provides 'additional' protection

2. What should you do if an RCD covering the kitchen keeps tripping out on a busy Saturday night?
Switch off all appliances. Switch them back on one at a time to determine which one is making it trip (assuming it is a faulty appliance). Stop using the faulty appliance. Call out an electrician.

2. What colour should the outside sheathing of a PVC ring main cable be under new regulations?

I am not aware of a regulation regarding the colour of the sheathing in a ring 'final circuit' (not a ring main, they are using the wrong terminology here), but cable sheathing is typically light grey in colour

3. Why does a TV have 3 amp cartridge fuses in its plug but an electric fan heater have a 13 amp fuse?

A TV will consume relatively smaller amount of power. If an appliance is rated at less than 700 Watts then a 3A fuse is recommended Watts = Voltage x Current therefore current = watts / voltage = 700W / 230V = 3 amps
A fan heater may be 2kw current = 2000W / 230V = 9 amps
Fuses come in 3A, 5A and 13A sizes. So you would need to use a 13a fuse for the heater.

4. What would happen if you got them the wrong way round?

if you got it the wrong way round, the TV could have a fault that would not be stopped by the 13A fuse, and the fan heater would keep blowing the 3A fuse because it is not rated high enough for normal operation of the heater.

answers in black above ^^^

 

[Spudnik]

10 brownie points for Mr ringer

 

[Silly Sausage]

Good answer from the ringer there!

To add to why is an RCD safer Q...
If one touches a Line(live) part, that's only protected by a fuse or MCB, the resistance of your body won't cause enough current to flow to blow the fuse/trip the MCB, so the circuit remains live with possible resulting death if you don't leave contact. An RCD will disconnect the supply within milliseconds @ a current of a few 10s of milliAmps.

 

[Silly Sausage]

1. There should also be an overall protection device that will trip all the power in case of a severe problem, this used to be an Earth Trip switch, but in modern consumer units it is an RCD.

Could argue with that one. I would say that the overall protection device would be the supplier's fuse.
Remember, RCDs are for additional protection.
'17th edition' CUs are dual RCD because everything has to be RCD protected now (domestic) & to provide some discrimination (RCBOs are best for that).

 

[HandySparks]

· How does an RCD work?

An RCD works by comparing the currents in the line an neutral conductors of a circuit (which, under normal circumstances, should be equal) and disconnecting the supply if the difference becomes too high. This would generally be caused by some of the current flowing to earth, for example via your body if you're unlucky enough to be touching a live part. Most, but not all, RCDs are sensitive enough and fast enough to prevent electrocution.

 

[supasparxs]

2. What colour should the outside sheathing of a PVC ring main cable be under new regulations?

Hi Steph,
There are several types of cables that can be used in creating a ring main such as a Twin and earth cable (Like you have in a house), FP200 Gold or generic (generally used on fire alarm systems but can be used for power and lighting), conduit (either plastic or steel) with singles cables within it. In recent years the colour coding of the wiring did change, but the colour of the outer insulation is unchanged.

I think either the person setting the question could have been unclear.

The reason why I suspect there is an error is because the outer insulation has not changed colours.

here is a piece that explains it a bit better

http://www.******************/Technical/DataSheets/Cable/CableColoursLeaflet.pdf

If I'm correct about an error the new live cable is brown, neutral is blue and earth core is unchanged as green and yellow

Richard

 

[Silly Sausage]

Hi Steph,
There are several types of cables that can be used in creating a ring main ....

Ring Final Circuit!
Don't lose marks for incorrect lingo.

 

[supasparxs]

1. What sort of consumer unit/fuse box does your establishment have?
· Is it a ceramic fuse block with different capacity fuse wire fitted?
· Is it a fuse box with large fuse cartridges instead of fuse wire?
· An MCB (miniature circuit breaker) style of consumer unit?
What are the advantages and disadvantages of each type of consumer unit?

Dependant on the age and the state of the wiring where you are working it's possible to have any of these. I think you should have a look at work tomorrow.

1) a rewirable fuse is cheap, can be a bit fiddly to rewire, possible to break the fuse-wire whilst fitting, when looking for a faulty circuit you may have to pull fuses that are live, the load the the fusewire will burnout is more of a guide, possible to replace fusewire with a piece of metal which is dangerous.
2) Cartridge fuses, easier to change, less likely to break whilst fitting, still need to pull potentially live circuits finding the faulty circuit. Cartridge fuse can overload by about 40% than the what is on the side of the fuse
3) Miniature Circuit Breaker are more expensive, normally work with electromagnetism, to trip at over current, easy to identify which circuit is faulty, easy to reset,

I hope this helps

Richard