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 Topic Title: 3 phase immersion heater Topic Summary: cable size and breaker Created On: 04 September 2007 11:15 AM Status: Read Only Linear : Threading : Single : Branch
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 04 September 2007 11:15 AM caboom Posts: 100 Joined: 13 April 2006 what size cable is needed for a 6kw 3 phase immersion heater and what size breaker? cable run less than 5 metres. 04 September 2007 01:37 PM rocknroll Posts: 9549 Joined: 03 October 2005 Hope this helps, or do you want us to do it for you? Cable selection procedure; 1. Determine the design current (Ib) of the circuit. 2. Select an appropriate size circuit protective device (In). 3. Apply correction factors (C) to the circuit as indicated. 4. Determine the effective current carrying capacity (Iz) and from the regulations find (It) 5. Ascertain the maximum permissible voltage drop and check the circuit voltage drop is in accordance with the formula: vd = mV/A/m x Ib x length ÷ 1000 6. Check the disconnection time of the circuit such that Zs(act) is equal to or less than Zs(Max). 7. Check the thermal constraints using the adiabatic equation. ------------------------- "Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"------------------------- 04 September 2007 02:29 PM Theapprentice Posts: 54 Joined: 04 August 2007 This is a trick question, isn't it?? 04 September 2007 02:34 PM davebarman Posts: 285 Joined: 27 February 2006 I assume that you are wiring it across 3phases and not linking it out and putting it across a single phase supply? regards dave ------------------------- Never knock on Death's door. Ring the doorbell and run like hell, he hates that! 04 September 2007 04:22 PM caboom Posts: 100 Joined: 13 April 2006 no. you guys do it for me. see what you all come up with. 04 September 2007 04:23 PM caboom Posts: 100 Joined: 13 April 2006 and yes wiring across 3 phases 04 September 2007 04:42 PM rocknroll Posts: 9549 Joined: 03 October 2005 Lets have your results first regards ------------------------- "Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"------------------------- 04 September 2007 04:51 PM caboom Posts: 100 Joined: 13 April 2006 i have no results thats why im asking for your help guys! come on you experts work it out and show your results.... 04 September 2007 04:57 PM Ricicle Posts: 894 Joined: 23 October 2006 If you give me a share of your payment for the job I'll work it out for you. ------------------------- Empty barrels make the most noise. 04 September 2007 05:10 PM rocknroll Posts: 9549 Joined: 03 October 2005 i have no results thats why im asking for your help guys! come on you experts work it out and show your results.... Why dont you give it go first, then we will help you regards ------------------------- "Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"------------------------- 04 September 2007 08:21 PM fredman Posts: 221 Joined: 26 July 2007 Me thinks that you are not going to get a reply, tell you what tell us how much you got in for the job and we can then add the consultancy charge and you can pay us before we help. xxxboys Naughty I shouldnt say that Edited: 04 September 2007 at 08:24 PM by fredman 05 September 2007 02:57 PM caboom Posts: 100 Joined: 13 April 2006 nope cant do it guys. so any serious takers out there? thought this forum was about helping each other out especially those still learning? 05 September 2007 03:06 PM rocknroll Posts: 9549 Joined: 03 October 2005 What do you mean you cant do it, have you worked out your design current yet? Do you knoe how to do it? A clue; Ib(design current) = kW ÷ √3Uo regards ------------------------- "Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"------------------------- Edited: 05 September 2007 at 03:09 PM by rocknroll 05 September 2007 03:07 PM caboom Posts: 100 Joined: 13 April 2006 no and no 05 September 2007 03:11 PM Theapprentice Posts: 54 Joined: 04 August 2007 Originally posted by: caboom nope cant do it guys. so any serious takers out there? thought this forum was about helping each other out especially those still learning? I'm learning but really this is rudimentary stuff 3 elements @ 2KW apiece how hard can it be Go on have a guess 05 September 2007 03:23 PM caboom Posts: 100 Joined: 13 April 2006 so theapprentice what size breaker and cable then?! 05 September 2007 03:59 PM rocknroll Posts: 9549 Joined: 03 October 2005 Design current (Ib) 6000 ÷ √3 x 400 (Ib) = 8.7 Amps Select circuit protective device, Type B 10A MCB Select cable, 1mm² Assuming no correction factors Voltage drop, 5 x 8.7 x 44 ÷ 1000 = 1.9 volts Assume TN-C-S of 0.35 Ze R1 + R2 from OSG page 158 5 x 36.20 ÷ 1000 = 0.18 ohms Zs = Ze + (R1 + R2) Zs = 0.35 + 0.18 = 0.53 If = Uoc / Zs If = 240 / 0.53 = 452 Amps Max Zs for 10 Amp MCB = 4.80 ohms Check for thermal constraints; Now who will check a 1mm² is okay, just the job for AJ Job done. ------------------------- "Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"------------------------- Edited: 05 September 2007 at 06:53 PM by rocknroll 05 September 2007 04:18 PM markLEDS Posts: 121 Joined: 09 August 2007 rocknroll, Would Ib not be (6000/3)/230 = 8.7a? 3 phase immersion heaters are commonly just a number of single phase elements, rather than 3 elements each with 400v across them. It makes hardly any difference, so Im splitting hairs really. Guess the answer should be to get the loads from the manufacturer. Mark 05 September 2007 04:36 PM rocknroll Posts: 9549 Joined: 03 October 2005 Ok, what if this is three phase and earth only no neutral, there are two fault conditions, phase to phase and phase to earth, is the 1mm² still okay. regards ------------------------- "Take nothing but a picture,leave nothing but footprints!"-------------------------"Oh! The drama of it all."-------------------------"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"------------------------- 05 September 2007 04:56 PM caboom Posts: 100 Joined: 13 April 2006 ok. we got there in the end!. so why is an niceic registered sparky saying to me that it should be 16A breaker and 2.5mm cable!!!!!!!!!!!!!
IET » Wiring and the regulations » 3 phase immersion heater

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