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# calculation

1. ### Single Cable calculation for hot tub?

Can anyone enlighten me on why my max Zs for this cable calc is so high? What am I missing?
2. ### No. Lights calculation?

Hello guys after some tips, what's your methods for how many downlights or regular lights you need for a room, do you use the lumen method from osg or any other method? I found this website: LIGHTING DESIGN BY LUMEN METHOD( WITH EXAMPLES): -...
3. ### Submain/RCD Selection

Hi there, I am new to this forum and I am finding the help very useful. Could someone please advice me on the following. So If I have a 60A Cutout fuse to the property how do you size the main switch, could a 100A be used. Also how would you size the RCD’s, why would one be 63A and another 80A...
4. ### Cable calculation - Derating factors

This is my first time here so please go easy 😂 I am currently designing some circuits for large convenience store and I have a question about the thermal insulation derating factor. A radial circuit will feed two display fridges, total load 10A. The circuit will run from the DB through the roof...
5. ### Formal Calculation of RCD Size.

I have had a good search for this information but can't find it anywhere not even in my on site guide 17th edition. So imagine you have a CU with 10 MCBs but no RCDs. You decide you want to install an RCD. You do your max load and diversity calculations for each MCB circuit and you come out...
6. ### Insulation Resistance Calculation

Hi, I have an engineer who is completing his 2391-52 exam tonight and he has been told one of his mock questions was wrong, I have completed the working out myself and came up with the same answer as him, so either the paper is wrong or something has literally left my mind!! "Determine the...
7. ### UK Three Phase wired machine ohms law calculation

I have a machine which is wired as 3 phase neutral and earth and is 15.1KW, there are no 415v components and all components are 230v, so effectively it is using 3 single phase circuits, however I have always carried out the circuit breaker calculation based on the 415V potential, I.E> 15120W...
8. ### Volt drop calculation and cable size

Hi A good friend of mine is having a large electrical installation carried out in his garden.Hes had 3 prices from various electrical contractors regrading the install. He is having a summer house built that will house 9kw 3 phase sauna 5kw hot tub 27kw 3 phase electric boiler A 32 amp ring...
9. ### Cable length calculation

Hi people, I'm carrying out an online course to gain my qld electrical licence. Been a good while since calculating cable length using equations and regs books. Can anyone guide me to the correct equations please Thanks in advance
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### Lost Neutral Voltage Calculation

I understand how to calculate the current in the neutral conductor on an unbalanced three phase installation, however am struggling to grasp how to calculate the voltage movement on each of the three lines if the neutral were open circuit. I appreciate it is influenced by the current and...
11. ### Volt sensing relay calculation

Hello, pls do no kill me for being this stupid (i am a videographer in nature :), and i need to make an order before my electrician returns from hospital... I want to add leisure batt to my 1987 VW t3 Caravelle along with volt sensing relay and i cant figure out how to calculate the system...
12. ### Stroma Certification Scheme SPD calculation / Stroma annual assessment

I've got my annual Stroma assessment next week and the job I am taking them to is a board change. I have not fitted an SPD as by my calculations it was not a requirement (plus a tight customer would not want the extra cost) I don't think it will be a problem but am just looking for reassurance...
13. ### Commercial Heat pump diversity calculation question

Hi, When calculating diversity. Does external air conditioning equipment such as heat pumps fall under heating and power in the osg such that you take 100% of the highest then 75% of the remainder? Thanks
14. ### Cable calculation

Il give you the scenario, stables in a field, e-on have been out and put a supply in a hut with a meter on and a one shot, main fuse is 80amps, the customer need a fuseboard putting in the barn, 75metres away, what size cable would i be looking at, ive done a calculation, 1 x swa cable 3 core...
15. ### earth fault loop impedance calculation

hello all could anyone help me i am doing my 2392 and i am a little stuck i have been asked a question which is using the following measured value of loop impedance 0.5 (40amp bs en 60898 type b mcb) ferfering to the maxium tabulated value given 1.15 show by calculation if the measured value is...
16. ### 10.5KW shower 10mm stud wall query?

So I have been working on a contract installing 10.5kw showers with B40 MCB's as specified by builders but occasionally a plot reports the shower tripping when having long showers. Hager don't do a 45A MCB but do a 45A RCBO but then its the cost....£££ The cable is ran in uninsulated studwork...
17. ### calculation check before i rip the flat to bits.

hi folks, got a CU change to do. flat rewired circa '70's. wylex 3036 fuses. my concern is earthing conductors. at present they are 6.0mm. TN-S. Pefc is 700A. not sure of main fuse size, so have taken worst scenario at 100A. referring to tables, @ 700A the disconnect time for a 100A BS1361 is...
18. ### GN8 9.3.1 Calculation of csa – armoured cable 118

Ordered GN8 not arrived yet anyone got section 9.3.1 Calculation of csa – armoured cable 118 to hand

20. ### Help cable calculation please newbe

I have a design unit and 14 circuits to do. Can some one please help as I have completed 1 of my knowledge and before I crack on any help on this would be great. It's a rough copy so excuse the mess. Thanks. It's question 4. Thanks
21. ### Calculation software

Hi All I’m looking for cable calculating software that would be suitable for commercial/industrial installs, can anyone recommend any please? Also any software/templates for estimating costs if possible please? Or is this something most people would put together themselves on an excel...
22. ### 95mm 4core SWA, just trying to go definitive on the steel to copper calculation

good afternoon guys I have a 95mm 4 core swa to this new office build , thats fed via a new exterior mains panel located next to a new sub station. now all feed cables on this project have been designed by an independent company, and i currently have flagged up that i believe that using just...
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### Calculation of capacitor value for conversion from star to delta

Hi does anyone have a notion of how to calculate the capacitance value for the above?
24. ### Short circuit calculation

Anyone able to help on the following... Short circuit calculation & current carrying capacity of: 50x10mm2 copper busbar & 80x6mm2 copper busbar One for the brain boxes..
25. ### 3-phase cable calculation

Hi, A while ago I posted about my neighbours 3-phase generator etc.... So he's being running through diesel like there's no tomorrow and been talking to a local barn who have said he can take the power from his property to supply their kiln. He's been measuring the his average usage over the...
26. ### Lighting Calculation Help

Looking some help with a question in an assignment I'm doing: A workshop with 175 watt low pressure sodium vapour lamp at 3 meters above the floor. The Sodium vapour lamp efficacy is 142.8 lumens per watt Calculate illuminance and 4 m to side of lamp Thanks in advance ;)
27. ### Cable Calculation for 2x25mm XLPE SWA

Good evening all. Just wanted some advice on a cable calculation, How do you calculate the carry capcaity of a circuit when there are two cables suppling a DB, we have 2x25mm XLPE SWA cable suppling a DB, just wanted to know how you would calculate the carrying capacity of these two cables...
28. ### Three Phase calculation

Hi, need to ask a question about a 3 phase air condition. On it's data tag it is rated at 20Amps. When it rated like this are the 20amps on each phase? Thanks in advance.
29. ### Cable Calculation Question

Hi there, Just after some advice for a submain/DB I’m quoting. A client has asked for a 12way TP board to be installed in a warehouse and the length of run is 150 meters. Section panel I’m coming from has a ZE of 0.05. MCCB will be a Square D CDAE 63A so max zs 0.68 at 5 second. Here’s my...
30. ### Cable size and protection - calculation

If possible could anyone have a quick look over these steps I've made myself for cable sizing and the protection needed. Please let me know if I've missed out anything. I also couldn't find a definitive answer for maximum permitted voltage drop percentage for 3 phase. I think it was 5% and 8%...
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### Completing Zs box on schedule of test results

When unable to carry out a Zs test on a lighting circuit (large/heavy chandelier type lighting), then the R1+R2 + Ze measurements are instead used and this is noted, but is it the norm to still write this value in the Zs box on the schedule of test results or just in the notes. I ask because...
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### Cooker diversity with SEPARATE oven/hob

Hi all, Looking at replacing kitchen. Current setup is 2.2kw oven, 5.6kw hob.. total = 7.8kw on 6mm cable, back to a 40a breaker. The current cable run is short.. 2m from CU, in breezeblock/plaster.. 2m clipped direct, to a 45a switch (for oven in tower).. 3m spurred from that, on...
33. ### Testing an off-peak board

How would I be best to go about putting a temporary supply to an off peak board for testing for accurate Zs readings? There is a board adjacent with a permanent supply.
34. ### Possible Job For Tomorrow

Reported as occasional trip of an RCD. Leakage current noted 2.5A when cooker switched on (which is on a 30mA RCD). Could be interesting.
35. ### MCS Requirements

Just trying to find out what requirements the MCS place on solar PV companies. A few come to mind but are they requirements or recommendations? Would be good to see a full list, does anyone know of one? 1. SAP calculation 2. Structural calculation 3. Correct system design 4 Panel testing...
36. ### pfc/psc manual calc

When calculation Zs how do I arrive at the PFC for that circuit, I know the tester works it out but whats the calculation formulae Pict
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### Help with breaker amp calculation

Hi, i need to know whether my calculation is correct. I have 4 x 2.2kW Motors (3-phase) , i have a miniture 32 Amp breaker (Type D) but according to my calculation i require a 40 Amp breaker. This is how i calculated it: 8800/(400x1.732) = 12.7 Amps per phase ---> 12.7x3 = 38 Amps Was my...
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### Volt drop three phase

When calculating volt drop on three phase, I can't remember if I my calculation is using the total current on all three phases or just each individual one. So each phase at 400v is 3.8A. My calculation was 2.5mm minimum. A three phase motor run in SWA. The run is 200M underground.
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### Harmonic filter problem ---- computer harmonic analysis using EasyPower software

I will just apologize to everyone in advance because of my English,, as well as for long post, I just don't know how shorten it :o.. I'm expirencing some problems (that are more "theoretical" nature) with harmonic filters.. I can't seem to find how to properly calculate the values for...
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### Volt Drop

This is a 2391 question DURING THE COURSE OF AN INSPECTION ONE OF THE SINGLE PHASE RADIALS supplying an item of fixed equipment is to be checked for volt drop. 45A full load, 80m length, 10mm singles,70 degree thermo singles, steel conduit, mohms/m at 20 degrees=1.83(p166 OSG)...