CK Tools :) The professionals choice when it comes to Electrical Tools
This official sponsor may provide discounts for members


  1. N

    Max volt drop for 25mm or 35mm feed to sub CU

    How does max volt drop for 25mm or 35mm feeds to sub CU work. Do we for example allow only 1% drop on the 25/35mm so we can keep 2% drop for lighting circuits and 4% for power circuits, or is there any where else in the regs that gives specific figures on maximum allowed volt drop? Any...
  2. D

    Max zs values

    Hey all im just trying to learn max zs values from a NICEIC chart i have, now learning these values isnt a problem but the sections reffering to bs3036 fuses and type D mcbs both have two lists of readings - one each for 0.4s and 5s trip times - where as the sections for type B and C only have...
  3. H

    Max continuity reading for bonding

    Good evening I was always taught the gas and water bonds should have a continuity ideally with a maximum of 0.05 ohms, is this a exact maximum or a rule of thumb and if it was higher than this what coding would we give it? I had a look through the codebreakers booklet but could not bit see an...
  4. B

    Max Tripping Time

    Would anyone know the max tripping time for this earth leakage device? I’m guessing 500ms it’s time delayed but I know that figure is for RCDs and RCBOs, I tested it at 560ms Thanks
  5. M

    Max Earth Fault Loop Impedance for OverCurrent Devices Before Amendment 3 and Now???

    Maximum Earth Fault Loop Impedance for OverCurrent Device was calculated 230/(MCB Rating*5) * Rule of Thumb is that correct? And how are they worked out now after Amendment 3?
  6. D

    18th edition RCD max disconnection times!!

    Hi all. I am seeing different figures here all over the net, table3a (p363) states a 30ma RCD has a trip time of 300ms max. So at 5x is the maximum 60ms? I seem to recall 200ms and 40ms for a 30ma and these are the figures I am seeing over the net... Please I just want the correct figures for...
  7. Baddegg

    Max permitted Zs values...

    Anyone know where I can find max Zs values for these?.....and the 6a LN 5906....
  8. C

    MAX Zs with 61009

    Why do we have maxuim Zs for 61009 RCBO's? I didn't think Zs values really mattered if the circuit was covered by and 30mA RCBO/RCD?
  9. stuarth

    Max demand & diversity advice needed

    I have been asked to do some work on a large 25 room mini mansion spread over 3 old properties made in to 1 with 6 consumer units on a single phase 100amp supply. The total loading of the breakers is 452 amps if I apply diversity at 40% I arrive at 180.8amps demand but this dose not take in to...
  10. B

    Max Zs TN system can’t achieve

    Sorry further on from last post, TNS system, Zs can’t be achieved on final circuits, getting 1.08 Zs on a B63 0.69 but protected by 167 ohms, poor design cable runs are too long and R1+R2 proves this, now I’ve spoke with my boss about what to record in Max Zs is it 0.69 or 167 ohms as all...
  11. E

    Output Max Amps

    What output current will I get if I have an input voltage of 700 volts at 1 amps and if I step the voltage down to 230 volts what would be the max amps I'll get.
  12. B

    TNS system Max Zs exceeded

    Local caravan site, 16/2C swa out have 3 or 4 Electric points with 2 x 16amp sockets on one circuit protected by B63 MCB now, TNS system Main RCD 100/300 mA protecting MCBs, now I’m testing and getting Max Zs of 0.99 when permitted is 0.69 so pointlet de rating to 50 amp, I don’t like the idea...
  13. S

    Doorbells again - volt drop / max bell wire length

    Hi Folks I've been trying to work out whether a doorbell will work with approximately 16m run of bell wire. I've tried to find out volt drop, resistance (to calculate volt drop), or even CSA of typical bell wire. But no luck. I tested an approx. 3m length with my MFT and got 0.87 Ohms. That...
  14. D

    Max Zs /ADS / shared CPC & N

    Hey Everyone. Whats your thoughts on using a 3core & earth to run x 2 final circuits? I have x1 three core & earth feeding contactors for emergency lighting. L1- fed from a 6A mcb is feeding a switched pole on a NO contactor, L2- fed from a different 6A mcb also feeding a pole on a NO...
  15. B

    USA 40 amp max pole?

    I am looking to add a 240v 50 amp circuit breaker to this panel for a welder. But (in the top left of the pic) is says that it is 40 amp max pole. Am correct to think this means i can only add a 40amp 240 volt circuit breaker?
  16. buzzlightyear

    need max for old mcb

    any body got the max ohms for old dorma smith mcbs , I asked dorma smith years ago sent me max ohms for old load masters .
  17. A

    Max Zs value for MCCBs

    Hi Guys, in an installation with one main Distribution board and several submain-DBs, do when you measure Zdb on a submain-DB incomer? and do we need to verify the Zdb value with the upstream protection device?( for example, a 250A, MCCB on the MDB outgoing). If yes, how can I get the max Zs...
  18. L

    Max Zs Permitted by BS7671 value

    Hi All, Thank you for welcoming to this forums I just want to clarify that the Value I need to enter 100% or 80% in the last column "Maximum Zs Permitted by BS7671" is it 80% from the table 41.3 from 18th Edition Regs - Page 62 or the value from Pocket Guide 18 Thank you Loges
  19. The apprentice

    max volt drop to sub board

    max volt drop to sub board 3 core swa 137 meters ?
  20. 1

    Max Zs @ 80% TN-C-S System

    Morning all, I'm currently finishing off my Lvl 3 C+G and I just need to finish off my design spreadsheet then I'll have completed it. I've one last column to fill in "Max Zs @80%" the design is based on a hotel using a TN-C-S supply. I'm just wanting to know where I can find this information...
  21. Ruairi Hansen

    Max zs readings for TT

    Hi just wondering what people are noting as there max permitted zs reading on test results sheet for TT systems? 200ohms or 1667ohms?
  22. P

    Domestic 45A breaker max Zs values

    Hi all, Why is there no max Zs value for a 45A type B breaker in table 41.3 of 18th edition? What value should be used as max value on schedule of test results? Cheers.
  23. happyhippydad

    Working on electrics with 2 supplies.

    I have little knowledge of PV. When working on circuits supplied by a domestic CU, is it fine to just have the main switch off in the CU or should you be isolating the PV as well? The stickers all over the CU's in this example all say to disconnect both supplies.
  24. HoverSPRX

    Commercial Max Demand/Diversity Query

    Hello All, Iv been asked to pick up the remedials on someone else's EICR that was done last year on a school for Deaf Children. One of the items listed on the report is the conductors leading to the sub mains from the main panel are undersized. I popped the cover off to have a look and sure...
  25. J

    Max Permitted Zs for 3036 semi enclosed rewirable fuse...

    I'm just hoping I can cross reference my knowledge or be corrected by someone on a quick query. It's a test question I'm doing but I'm querying the answer I've been given. I want to find the Max permitted Zs on a 3036 45A fuse. I was under the impression that I should reference table 41.2 in...
  26. C

    Commercial Max disconection times

    Having a debate on site as to disconection times on a TN system, does the 18 addition say 0.4 up to 32amp and 5 after and 5 for distribution circuits?
  27. B

    Max Zdb TNS system help

    TNS system Ze is 0.3 ohms all good now sub mains is fed from this but I’m getting 3.15 ohms still should be under 0.8 ohms? Thanks
  28. C

    Diversity applied, max load well over.

    Seen a couple of threads on diversity and excessive max loads recently. Just had a design from a clients for their house. Applied diversity is 196A. Having 2 9kW showers install, A 4kW instant water heater, a cinema room, ring main per floor, lighting circuit per floor and ring main for...
  29. M

    60A Fuse box - is (typical) over 60A max load OK?

    This relates to one of those old 60A Wylex Fuse boxes that has been upgraded with MCBs - I know it would be a very good idea to upgrade, but the question is, how does the "Max 60A" rating moulded on the box apply? The main fuse is 60A and the load after diversity calcs is 89A. I am aware that...
  30. B

    Max Demand for mixed use commercial units

    Hi, Looking at a potential job. Agricultural buildings being divided into 10 mixed use units of around 1000 sq ft each. Present supply is a 100A TPN incomer. Future use of units is unknown at this stage, but planning is for B1 B2 so uses could be anything from a warehouse with a bit of lighting...
  31. C

    Max zs on double pole mcb

    I am filling out test sheets and have a merlin gerin D32 C60 HD double.pole mcb. The rating on the mcb says 415V feeding 2 feeds to a canalis busbar. BS7671 States max zs for D32 0.4 secs is 0.34. Is this just for single pole MCB? I have also check my max zs value from manufacture stating...
  32. B

    BS 7671 max surface temperature under fault condition ???

    Can anyone give me some clarification on the following. I am installing some Osram Planon Plus led light panels into a temporary building and have been told the transformers need to housed in an enclosure as they do not have the correct markings for BS7671 "max surface temperature under fault...
  33. jackhammerJIM

    Commercial sub mains exceed max zs of mccbs

    Thoughts required on todays scenario . Commercial premises fed from 100 amp 3 phase TNS supply ZE 0.40 feeds 80 amp 3 phase switch fuse (max zs 0.57) feeds 400 amp mainswitch protek panel in 35mm swa 16mm earth 125 amp mccb (0.24 max zs) submain exceeds max zs at 0.57 Had this down as a...
  34. spud1

    What if a circuits Max Zs is exceeded but the circuit is protected by an RCD?

    Just processing an EICR and noticed a couple of final circuits measured Zs values (fed from a sub distribution board) slightly exceed the Max permitted Zs values for the OCPDs that protect them. Obviously I will note this as a design flaw in the observations, but I just wondered, from the...
  35. S

    Industrial max zs for 1492 and 1489 allen bradley breakers

    Hi we are using allen Bradley 1489 and 1492 range of circuit breakers, and I cant find the max zs values on any of the data sheets, does anyone have a list of them? Many thanks
  36. gazdkw82

    Maximum Zs values for BS3871

    Where can I find the max Z's value for a BS3871, type 3, 32A MCB? Iv had a look through BS7671 and done some searching online but I cannot find it. IV found some tables with listed Zs values for a 3871 but I have no idea where they originate from or how old
  37. Lekky1

    Exceeded max demand questions

    Hi guys, I have been asked to fit a ring main in a utility room currently being built with a outside socket and a lighting circuit with 4 led lamps and a outdoor light, this much I am comfortable with. My issue is with the max demand, The current consumer unit is loaded to the max with 212amp...
  38. haptism

    Varilight Dimmer max loading

    Hi, hope someone can advise. Ive just called Varilight helpline in regards to max loadings on their 300w trailing edge LED single gang dimmer. They tell me that I can have a maximum of x30 10w leds on the dimmer. Most info out there regarding dimming LED suggests to divide the dimmers wattage...
  39. D

    Max Zs on certification

    Please can people clarify what value they insert in the Max Zs field on certification. I've always input 100%. Currently in disagreement with another person as they are specifying 80%. Done my 2391 in 2008 and I was taught and told it's always 100% and it's down to the QS to interpret the...
  40. J

    max demand for 12x all elec flats

    starting 12x flats next week that will be all elec -with a rather juicy electric boiler (12kw)- havn't won the intake/communal work yet- but just doing my pricing for it ready does my maths look good for working out the max demand and kva of main supply- currently it is only 100a TPN so around...
Top Bottom