This official sponsor may provide discounts for members

# calculate

1. ### How do i calculate missing resistance readings in a parallel circuit using R1 and Rt

Hi I am a current student studying to become an electrician and a question has thrown me. I'm wondering if someone could help, there is a question on one of my home work books. "complete the following table assuming the resistors are connected in parallel?" the example I will give is R1 is 120...
2. ### How do i calculate the total resistance in a series-parallel circuit?

Hey, I'm an electrical engineer in training and i was wondering how you could calculate the total resistance in a series-parallel circuit? I attached a picture of what it looks like. If it's to any help resistor 1 is 2, r2 is 3, r3 is 4, r4 is 5 and r5 is 6 Ohm. Thanks for any help
3. ### How do I calculate the resistance of a spur without phisically testing ? ..

Boffins of the electrical world ... How can I calculate the resistance of 48m ring 2.5/1.5 .. with a 8m spur .. I can quiet easily do this without a spur in the equation but , my test papers require my doing so with an 8m spur. . how does this affect the zs tests ... Thanks v much ...
4. ### Calculate device/battery run time

Hello I am trying to calculate how long a car battery will last for which is 50ah, 12v. Running a 20watt device, 240v, turned on 24hours a day, how long would this battery last? Any help appreciated thanks
5. ### Can I calculate how fast an RCD should trip?

Hi all. Been bugging me. I think there is a way to calculate how fast a particularly rated RCD should trip (rather than measuring) but I can't remember how to do it ? e. g. If I was designing an SWA submain fed from a TT earthed installation and I needed to install say a 300mA TD RCD to...
6. ### Measure or calculate your Zs?

Hi again! Which value is best to record in a certificate or report, a max measured or a calculated Zs? I know Sparkies who do it both ways, but personally I take measured values at all the points of utilization to find the highest, then I calculate Ze+(my highest R1+R2) for the circuit and...
7. T

### Calculate this...Part II some pics of the main cut-out and fuses

Yeh so thought I would check the main fuses and still can't tell what rating they are. I did contact the man from the DNO who said no hurry the next few months will do. @Leesparkykent he did say there are no penalty charges right now but come April there will be. We spoke with the energy...
8. T

### Calculate this. Just got this letter emailed to me...

Errr I am going to contact the guy in the letter. This is not a new supply they have been supplying the place for 30 years to my knowledge. But do they really expect me to calculate the load on maybe 70 DBs and then apply diversity to 66 different businesses??? Bit of a tall order unless I am...
9. A

### How to calculate the tabulated current (It) for circuits with multiple Reference Methods (A and B)?

I am trying to select a suitable conductor size from Fig 4D1A of the BS 7671 Book, and am encountering a problem because the circuit does not conform to one Reference Method. The circuit conductors leave the distribution board in wall mounted steel trunking, then run through some steel conduit...
10. ### Distribution board checks

Hi I have a question regarding switch boards and distribution boards. We have an existing switchboard and we want to use four spare ways in this to feed three new tp & n distribution boards. One for lighting one for small power one for security services. My question is what calculations have to...
11. A

### From Voltage Source to the Machine

I have a project assigned to me, i.e. to calculate/compute the wire size, length, put a motor control in a Plastic Machine. I have some sources available, but still I want to know from the best people of this Forum. Please assist me on how to compute the wire size, wire type, type of controls...
12. A

### 3 phase 4 wire Neutral Calculation.

Hi all, Im still in apprentice stages of becoming a sparky and currently learning allot about 3 phase at college the moment. Can anyone share their knowledge with me on how to correctly calculate the Neutral current on a 3 phase 4 wire star system when there is an imbalance between phases e.g...
13. E

### testing zs - EAWR

on an eicr is it right or wrong to test for zs or is it putting us at unneccassary risk of shock ?? If the regs say we CAN calculate using Ze+(R1+R2)measurements taken during dead testing then SHOULD we?? ! anyone any clear cut answer on this 1??
14. P

### Voltage drop

Hi all If an outdoor circuit comprises 2.5mm SWA running to adaptable box where it then splits into 2 x 1.5mm SWA cables for lighting, socket etc. how is the VD calculated? I presume the VD for the 2.5mm run is calculated up to the adpatable box and added to the 1.5mm VD for each additional...
15. M

### R2 Testing Help

Hello i havent done much testing before so i am trying to brush up on my Testing skills before i join Elecsa, i have a couple of questions about R2 testing please. I understand how to carry out R1 R2 tests using method 1 and that we do them to calculate the Zs of our circuit Zs=Ze+R1+R2 But i...
16. M

### Cable Mate Software

Hi is anyone on here using the cable mate software? Ive just bought it, just waiting for my registration code to come through. It looks very good. Cable-Mate This software will calculate the minimum cable size for copper cables up to 1000mm². It also allows you to: Check Disconnection...
17. M

### Conduit as earth????

Hi all done some testing work at a hospital and the orignal wiring was done in metal conduit, now the zs figures tested all good, my question is can u calculate the r1 and r2 figure when their isnt an earth cable as such???
18. ### Megger Mft 1730 calculating R1&R2?

A student of mine had his new toy delivered today (delivery first thing, thank you very much Tester Meter). We've had a play with it and I am surprised to see that it has a method of caculating R1&R2 as what appears to be normal practice. You turn the dial to Zref, make a loop impedance...
19. N

### Who does just a Zs when carrying out a periodic on a lighting circuit

Just answered a question on another post ,and it dawned on me , yippee the brain kicked into gear , i have read on loads of posts that people say doing an inspection just calculate the R1R2 by doing a Zs and taking away the Ze , i have never liked this method and heres a reason why ...
20. ### Help checking lighting circuit

Hi Guys When checking a lighting circuit you obviously need to check at each point on the circuit, switch and light fitting. What do you do when you can't get to the cable in the light fitting?? For example, in my kitchen I have 3 spot lights on a bar. I'm not able to remove the bar...
21. N

### Calculating 3 phase kva

My brains switched off chaps and i can remember how to calculate 3 phase kva i know its V x I x 1.73 / 1000 so is it 230 or 400 x I x 1.73 / 1000 fee a right numpty cant belive ive forgotten it not done 3 phase calcs for a while please enlighten me to the correct figures then ill give my...
22. ### Can someone tell me the power consumption of a 110V Tranny when off ?

I guess if I knew the resistance of the Primary coil I could calculate it ? but wondered if anyone had a reference guide to current consumption when a 110V tool is not in use ? ATB Steve
23. S

### volt drop or not

Hi all My question is this If a submain is run off the No.1 C/U to a No. 2 C/U, when we calculate the cable sizes for the C/U2 final circuits do we use the volt drop value of the sub main or do we use the 230v value ??? thanks for any help john
24. P

### Zs testing

Just wondering if everyone actually does a Zs test when filling in a schedule of results. In the OSG it says that you can measure it or calculate it by addition. I appreciate the different value stuff, just thinking it is a lot easier and quicker to be adding 2 figures together than taking...
25. G

### Verification of volt drop

Hi, I know how to calculate volt drops on radial ccts, As a ring main is a loop and you ignore any spurs is there a voltage drop or is it considered to perfect or near perfect mains voltage regulation!. How do you,or dont you verfiy votage regulation on a ring main when certifing that you...
26. ### Prospective Fault Current

Hi Guys How do you calculate Prospective Fault Current?? Wouldi be correct in thinking it is nominal voltage divided by Zs + R1 + R2 ??? So Nominal Voltage Zs + R1 + R2 A