electical and mechanical questions

[Miley4321]

okay ill try this a different way as my first way wasn't considered acceptable. Hi everyone I have recently joined this forum hope everyone is doing okay. I have a few questions I am currently on a uni course in which I have completed my assignment apart from two questions which I am finding hard to locate the answer via the internet and the lectures just don't have the time of day to help us. The questions are as followed : select a protective device for the following and justify selection: 1. socket circuit supplying the office 2.circuit supplying a conventional machine 3.supply to a welding set and the second question is design a network suitable for the office / workshop, taking into account WAN / LAN , cable selection, interference and data loss. Please realise that I am not just posting these and expecting people to answer them I am just looking to be pointed into the right direction of where I can find my answer thank you everybody.ddd11 dffffdd

 

[Plonker 3]

What sort of ideas do you have at the minute in regards to the answers?

 

[Miley4321]

this is what I have on the socket circuit: The 17th Edition requires socket-outlets rated at up to 20 A and intended for use by ordinary persons to be provided with additional protection by means of a 30 mA RCD. However, the offices will have computers producing protective conductor current, individually and/or collectively. This accumulated protective conductor current could cause the circuit RCD to operate. Such disruption will not be acceptable to the office. To fix this potential problem, unwanted tripping can be avoided by appropriate sub-division of circuits. I will not use rewire able fuses on these as for the welding and conventional machine is where I am struggling and as to the second question on cable selection am thinking of going for a cat 5e , I have no idea for the WAN and LAN and interference of data loss I will but a repeater in after 100 meters of cable used to strengthen the signal .

 

[Plonker 3]

Seems as though have a grasp of the basics of what you need. Do you have a copy or access to a copy of the current wiring regulations?

 

[Miley4321]

i do have the basics I just carnt find any advice on what protection to use on welding and conventional machine my initial thought would be to use an rcd for life protection but apart from the life protection i don't know how else to justify it . unfortunately a don't have a copy .

 

[Plonker 3]

Well depending on the loading of the welder you could always hard wire it into a isolator, avoids the use of any socket and any RCD, unless the manufacturer states it needs RCD protection.

 

[Silly Sausage]

Need Regs, try here...

http://www.electriciansforums.co.uk...nly/72549-downloads-section-2.html#post830651

or this if you can't access the above
https://www.copy.com/s/Uf2JcuFNhX4z/BS%207671_2008%20%282011%29%20Requirements%20for%20Electrical%20Installations%2C%20IEE%20Wiring%20Regulations%20%E2%80%93%20%2017th%20Edition.pdf

 

[Miley4321]

when you say depending on the loading , how do you mean ? i'm liking the idea of wireing it seperatly and the manufacturer will not be a problem because it is just a general welder. Unfortunatly it will not let me view that page.

 

[Plonker 3]

Well a welder would require its own dedicated circuit. Although if you were to put it on a 32 amp plug then it would not require RCD protection then, unless used outdoors.

 

[wozz]

out of interest what uni course is this you are doing?

 

[wozz]

how much detail do they want are they expecting a circuit design with calcs?

 

[Miley4321]

i am doing a building services degree which is basically a basics of everything electrical plumbing renewables project management business plans etc so i will not require calculations on these parts , i have already done other parts that require calculations for example when installing a lift i have done calcs such as Population

10 m[SUP]2 [/SUP]Per person

Population = Floor Area / M[SUP]2 [/SUP]per person

1000m[SUP]2 [/SUP] / 10 =

100 people per floor

There are 10 floors however the ground floor is classed as terminal and will not be used meaning that all together we will calculate for 9 floors. This means altogether the total population would be 900 people.

I will reduce this number by 20 percent due to shift work etc.

This means there will be 720 people altogether.

Peak traffic:

Arrival rate = 12 to 15 percent to use lift at one time
Assume 14 percent of the people will want to use the lift at any given time.

12.5 percent of 720 =90 people

This means we are looking to move 90 people within 300 seconds.

We will take a good arrival rate to be within 30 seconds (300 / 30 =10)

This means 10 trips will be required.

Peak travel

Number of trips = 10

Number of people= 90

To work out people per trip we do number of people / number of trips.
= 9 people per trip

Now a will increase 9 people by 20 percent = 10.8

This now means I have a car that’s capable of carrying 10.8 passengers per time.

1. Calculate the return transit time and estimate the size and number of cars needed.

RTT (Return travel time) = 2H Df / V + ( S + 1) (TC =TF (1) +TO DF / V) + 2 PTP

H= Average highest reversal floor.= 7.9
Df= Average interfloor height in meters. 3.3 meters
V= Is rated speed in meters per second. 1.6 seconds
S= Is the average probable number of stops.= 3.9
TC= Is the door closing time in seconds.= 2.5 seconds
TF(1)= Is the single floor flight time in seconds.= 5 seconds
TO= Is the door opening time in seconds= 3 seconds
P= Is the average number of passengers in the car.= 9
TP= Is the average passenger transfer time in seconds.= 1.2 seconds


TC + TF (1) + TO = T = 10.5 seconds

Find TV

Total distance = Number of floors x Interheight
9 x 3.3m = 29.7 meters.

Max travel in 30 seconds = 48 meters
Rates speed = 48 / 30 = 1.6 meters per second

TC + TF + TO = 10.5 seconds

To simplify DF/V into TV = 3.3/1.6= 2.06 seconds

Find T- TV = 10.5 – 2.06 = 8.44 seconds

RTT simplified = RTT= 2 x(psi TV) + (S +1) (T-TV) + 2PTP

 

[wozz]

I have not done a degree and the question is vague but this would be my take on it:

ok not too much detail just cover your arse with 'without knowing more detail of installation and supply ect ect'

sockets i think they would be looking for you to go down the RCBO route, borrow a copy of the regs and support your decisions with reg numbers regards <20A sockets.

Conventional machine, follow manuf instructions and look for rating plate and use this to size a MCB. BTW i have no idea what a conventional machine is i take it they mean one without inrush so just a resistive machine.

Welder, again follow any relevant manuf instructions, welders will have a fair bit on inrush usually so you will have to size a MCB but also consider type C,D to account for this inrush.

You could support your argument by including some welder instructions which may state a MCB type or details of the inrush.

I dont think they will be after any numbers just a thought process and identify factors to which would lead you to a answer with more detail.

 

[telectrix]

also, bear in mind that for the offfice. sockets that are not intended for general use and under the control of skilled or instructed persons do not require rCD protection. however, computers would require a circuit with high integrity earthing.

 

[gnuuser]

because you are designing for the office network consider using shielded cabling for your cat5
fiber-optic would be better here though.
and emi noise filtering in your power for the office
also consider a good ups/ or power conditioning system to prevent spiking or brown-out (when welding operations are going on.
wireless could be a problem if too near the welding shop as some inverter based welders can emit high frequency interference.

probably not the answers your looking for but just something to take into consideration!