Need Help From Electrician

[MrLaoKao]

Hi all!

I'm building a small garage and it is soon ready. Unfortunately I have problems finding a real electrician here south of Udon.

The guy building the house is asking me what cabels I want, and that scares me.

Anyhow I have a 15(45)A meter at the electrical pole outside the land. (Does the 45A denote some kind of maximum usage?)

I have a panel with a 65 A main circuit breaker. The electricity will be brought into the house underground. The distance is about 60 meters. What dimension do i need for the cabel underground?

Thanks for all help!

/MLK

[bankruatsteve]

Are you wondering what cables to the house or the garage?

As for meters, I don't know if anybody really knows what the specs are for LOS, but what you say seems to be the accepted.

I too have 15a meter with 60a main breaker and the PEA said to use 25mm2 AL from the meter to my CU. So, that's what I did (and that should support 60a just fine). Underground shouldn't be much diff but you need to have it in solid conduit.

If you are just tailing off from your house to the garage - and it's not too far - you should be able to use the normal 2.5mm2 cable for 20a circuit (and should be with ground - I use the green 1mm2 for that).

[stgrhe]

The underground cable should preferably be a copper cable of type NYY and run in the black PE cable run. Suppliers of NYY cables are Bangkok Cable and Thai Yasiki.

The indoor cables should be of type THW.

The cable sizes (cable areas) will depend on the load in addition to the 60 m lenght that you have mentioned. The recommended maximum voltage drop should not exceed 5%.

[MrLaoKao]

Bangkok Cable Company has info about their cables and gives a small guideline in current ratings.

http://www.bangkokcable.com/catalog/BCC_CATALOG/NYYG2EN.HTML

Edited July 18, 2010 by Crossy
fixed the link

[elkangorito]

I'm a bit confused.

First you say this, "I'm building a small garage and it is soon ready", & then you say this, "The guy building the house is asking me what cabels I want". You then go on to say, "The electricity will be brought into the house underground. The distance is about 60 meters. What dimension do i need for the cabel underground?"

Questions:

1] How many buildings are you talking about? From my understanding, there is a house (under construction) & you wish to add a garage.

2] Do you want to know the cable size for;

a] the cable from the street to the house? or,

b] the cable from the house to the garage?

BTW, the info in the above link is of little use at the moment.

Edited July 18, 2010 by elkangorito

[electau]

If 45A is the max demand and the route length of the consumers mains is 60 metres you will require 25sqmm min. Cu.

If the max demand is the setting of the MCB ( 60A/63A) the size will be 25sqmm.min.Cu.

Those figures are for a 3% voltage drop between the point of connection to the consumers mains and the main switchboard.

Allow up to 2% voltage drop within the installation.

Ref. AS3000.

　

　

Edited July 19, 2010 by electau

[Pib]

The 15(45)A means 45 amps is the meter's max rating and the 15 means the meter's test amperage point for accuracy. Actually, when meters are tested for accuracy they are checked at various points but the test amperage is the primary test point. Usually the test amperage rating is "approx" 1/3 of the max rating like a 30(100)A meter which means 100 amps max with a test amperage of 30 amps. Meter manufacturers can pretty much pick the test amperage rating, but they seem to choose a number aroud 1/3 of the max rating, which some may say is the average 24/7 current a household will draw with a properly sized electrical system/meter.

[WarpSpeed]

Lots of mentions of voltage drop in the above posts, certainly you mean to say amperage and not voltage as with A/C the voltage will be consistent no matter what the distance is but it's the amperage that fluctuates according to load and cable size.. I.E. 240 will still be 240 if tested regardless of line size or load..

[Pib]

No, you will have a voltage drop due to cable resistance caused by construction of the cable, heating from amperage draw, etc. Also, as the line resistance goes up you also have a reduction in current/amps since the input voltage of 220V remains constant from a well supplied transformer feeding the area/home..

Regarding the voltage drop and to use an extreme example, a break in the line from the pole/meter to the house would be the same as super high/infinite resistance with no amperage flow. E=I*R. 0 amps times infinite resistance equals zero volts....or a total voltage drop and no current flow. Now you would still measure 220 volts at the pole/meter, but after the break in the line you would measure zero volts.

Edited July 24, 2010 by Pib

[Khonwan]

Lots of mentions of voltage drop in the above posts, certainly you mean to say amperage and not voltage as with A/C the voltage will be consistent no matter what the distance is but it's the amperage that fluctuates according to load and cable size.. I.E. 240 will still be 240 if tested regardless of line size or load..

Huh???? My voltmeter shows very significant reductions when I increase the load!

[WarpSpeed]

^

Then you got electrical issues you need to deal with..Your amperage will drop but not your voltage.. It remains at 240 and that also goes for the post above you..I can have every appliance on in my house and will still read 240 volts at the source..

Edited July 24, 2010 by WarpSpeed

[WarpSpeed]

No, you will have a voltage drop due to cable resistance caused by construction of the cable, heating from amperage draw, etc. Also, as the line resistance goes up you also have a reduction in current/amps since the input voltage of 220V remains constant from a well supplied transformer feeding the area/home..

Regarding the voltage drop and to use an extreme example, a break in the line from the pole/meter to the house would be the same as super high/infinite resistance with no amperage flow. E=I*R. 0 amps times infinite resistance equals zero volts....or a total voltage drop and no current flow. Now you would still measure 220 volts at the pole/meter, but after the break in the line you would measure zero volts.

Poor example it goes without saying, if a line is in tact though you have no voltage drop nor would you have any voltage drop at the site of the break on the pole side but conversely you can have a break that still makes contact but can not carry load so you will read a voltage of 240 but it will not operate any appliances even a light bulb this is how you check a broken line if you still have voltage readings you put it under load and read the amperage or it will not run at any point..

I'd like to add the caveat that these are in proper cable and wire gauge application scenarios and if you have other then you are not properly spec'd for your load considerations..

Edited July 24, 2010 by WarpSpeed

[elkangorito]

There is too much 'misinformation' here. Besides, the OP hasn't been back to clarify exactly what he is talking about.

In the meantime, cable length & voltage drop are proportional quanities...the longer the cable, the greater the voltage drop.

[Khonwan]

^

Then you got electrical issues you need to deal with..Your amperage will drop but not your voltage.. It remains at 240 and that also goes for the post above you..I can have every appliance on in my house and will still read 240 volts at the source..

I know that I have problems: 1 mile of 50mm cables (as advised by the ever helpful PEA) between house and transformer. My point is voltage can drop – though I see you now cover this with your caveat in your next post.

[electau]

^

Then you got electrical issues you need to deal with..Your amperage will drop but not your voltage.. It remains at 240 and that also goes for the post above you..I can have every appliance on in my house and will still read 240 volts at the source..

I know that I have problems: 1 mile of 50mm cables (as advised by the ever helpful PEA) between house and transformer. My point is voltage can drop – though I see you now cover this with your caveat in your next post.

I mile ( 1.6km ) of 50mm copper conductor, yes one will have voltage drop depending on the demand, was this over one phase only or balanced over 3 phases and neutral?

One was surprised that the PEA did not extend the HV line and install a distribution transformer closer to your property line.

What is your max demand in amps per phase?

Voltage drop is measured from the point of connection of the consumers installation, voltage drop on the distribution network is calculated separately.

[Khonwan]

Hi Electau

I have a 50kVA 3-ph transformer. I ran (as my ‘own contractor’; PEA only installed the transformer, two required posts, meter, and completed connection) 4 cables 50mm² just short of 1,500m (I had purchased and collected 4 drums of 50mm² x1,500m plus 1 drum of 25mm² x 2,000m straight from the factory) to my main breaker in my tractor shed with remainder being run on towards my house, being reduced to 25mm² 56m before reaching my house (I have additional small houses and outbuildings serviced with the remaining 25mm² branched off from the main breaker), i.e. 50mm² x 1,500 plus 25mm² x 56m between transformer and main house.

I had already had a PEA survey 5 years before which quoted a cost of 720,000 baht for HV to a point 150m from my house plus 30kVA-1ph; it seemed likely that that the cost would have risen by another 200,000 baht by the time I decided to proceed (I relied on a petrol then diesel generator for several years). Since I owned all the land, the current location of the transformer is indeed within my property line – I (my wife, for the benefit of the purists) own and farm 200 rai (80 acres or 32 hectare). Doing it myself cost ‘only’ just under 400,000 baht - a likely saving of at least 500,000 – and did not encourage others to build near me.

Several PEA managers had already been out to my house (as a result of my complaint to the PEA’s head office in Bkk alleging corruption on the part of one of their employees) and knew exactly what I wanted to achieve. I specifically told them that my maximum demand was 17kW (total). They knew that I only had single-phase appliances. They knew that I did not want to pay nearly one million baht only then to have neighbouring field owners build houses next to me and attach their transformers without any reimbursement to me for the HV installation costs. They agreed to install the transformer at a particular part of my property line adjacent to one of their existent HV lines. They were told this distance (selected transformer-location to my house) was around 1,500m. They told me I would need 3-ph in consequence of this distance – yes, Electau, I hear you laugh here. Since there was only 1-ph HV, I had to pay 50% of the installation of a third HV cable over a distance of around 4.5km (I’ve included that cost within my B400k above).

I had already composed a simple equation to determine voltage drop (I had no access to Internet at that time and therefore could not access online calculators, or forums) but could not get anyone in PEA to look at it. I told them that my equation returned a drop of 21% on a balanced load of 17kVA (assuming no load voltage of 235V) resulting in 190V but they said “three phase will not drop” (in Thai, of course). I told them I had no experience with 3-ph but could not understand how 3-ph would prevent such a drop in respect of 1-ph appliances. “Three-phase will not drop” was their only reply...their mantra. Still not trusting my local office (Lat Yao, Nakhon Sawan), I drove to the MEA HO in BKK to speak to an engineer. I was advised they had none there so was sent to their Klong Toey office to speak to the engineer there. Said engineer was disinterested upon learning we were from Nakhon Sawan – he also refused to discuss my maths, sticking instead to the aforesaid mantra. Three weeks later, and with nobody I could go to for advice, I capitulated and signed the contract on the basis that these supposedly qualified PEA and MEA engineers must know more than me (!).

Upon installation, my equation checked out correct (I used a one-way cable length of 1,612m of 50mm² for my equation, i.e. I treated the additional 56m of 25mm² as 112m of 50mm²; appliances rated at a total of 5kW were operated on one phase and resulted in a metered voltage of 195V; no load was metered at 235V); I demonstrated this to the local managers at my home. One idiot (later, in their office) pulled out specs books and decided I should have had a 30kVA 1-ph and that that would provide my 17kVA max demand using only two existing 50mm² cables. I told him this was incorrect (nicer than “stupid”). They said they wanted to try it – they decided to experiment by temporarily swapping my 50kVA-3ph with an available 30kVA 1-ph transformer. I invited them to double up on the cables, effectively running two 100mm² cables – I then told them what the resultant voltage drop would be based on my equation. They came, they swapped, they checked, they agreed I was correct, they swapped back, they went home. Later, another PEA chap studying books eventually stated that I should have run 95mm² cables – I agree with this completely.

Their only solution was for me to pay them to run HV to within 700m of my house – I refused since that would mean me agreeing to simply write off the 2,400m (1,500-700 x4) cost of 50mm² plus posts that they had caused me to install.

I can currently use only 3.2-4.0kW per phase without the voltage dropping falling below 209V (acceptable 5% drop against 220V nominal voltage for Thailand) and this only because I get 235-240V from each phase at the transformer (not balanced even at no load). In consequence, I have a 12kW 3-ph shower heater, 3-ph welding unit, 3-ph high-powered water sprayer, and have ordered a 3-ph 3hp submersible pump for a borehole I’ve just had drilled. In consequence, I manage well (rarely experiencing very-significant voltage drops) within my electrical limitations.

I am now, some 4 or so years later, on better terms with my local PEA after a change of manager...and after a complaint to PEA’s CEO on a matter of billing (I was proved correct).

For the benefit of anyone else with the patience to read this far, 380-415V (3-ph) experiences only insignificant theoretical voltage drop in this type of situation but a 3-ph set up is no better than simply doubling the size of your cables in a 1-ph set up in respect of single phase appliances, i.e. 50mm² x 4 (3-ph) would provide no more 220V supply than 100mm² x2 (1-ph), where you have your own transformer. A 30kVA 1-ph transformer and 1-ph meter are cheaper than 50kVA 3-ph transformer and 3-ph meter (those transformers are the minimum rated that PEA will install – at least, that’s what they told me); 100mm² x2 is cheaper than 50mm² x4; installation is easier and half the brackets are required.

My equation:-

For Aluminium: Resultant voltage=V-(((0.028633*(1.004^(T-20)))*(L*2)/S)*(P/V))

For Copper: Resultant voltage=V-(((0.0180909096*(1.004^(T-20)))*(L*2)/S)*(P/V))

Where V is no-load voltage (volts), T is ambient temperature (°C), L is one-way cable distance (metres), S is cable section (mm²), P is power (watts).

Regards

Khonwan

PS. I’ve posted on aspects of this before.

[electau]

Wait until I do some calculations Khonwan on what you have given me and I will be able to answer your questions.

[electau]

This may be of assistance to you Khonwan.

I have based the calculations on 230/400V 3 phase 4 wire supply.

Transformer size 50kVA, 72A per phase. Total load 17kW. Load is all single phase connection. Conductors are copper.

Load balanced across the 3 phases as closely as practicable for the purposes of calculation.

Phase A 5.6 kW (25A)

Phase B 5.6 kW (25A)

Phase C 5.6 kW (25A)

Route length from Transformer to MSB 1500M. 50sqmm copper x 4.

Route length from MSB to DSB at house 56M. 25sqmm copper x 4.

Permissible voltage drop 7% as the transformer is dedicated to one installation only.

For the purposes of calculation 5%( 11.5V) to the MSB and 2%(4.6V) from the MSB to the DSB at the house. Total voltage drop 16.1V.

For a load of 7.5A per phase at 230V for a voltage drop of 5% over 1500M the minimum size of copper conductor would be 50sqmm.

Calculations based on AS3000.

A 17KW 230V load connected on a single phase transformer would be 74A and the cable size for 5% voltage drop would be cost prohibitive and not practicable on a cable run of 1500M.

It is obvious that the PEA did not do any formal calculations on voltage drop based on your connected load.

The resistance in ohms for 50sqmm copper conductor is approx. 0.43 ohms per 1000 metres.

Length 1.5km *2 * 0.43 = 1.29 ohms. Voltage drop for 7.5A is 7.5*1.29 = 9.675V.

Voltage drop for 25 Amps would be 1.29 * 25 = 32.25V. The voltage at the MCB at the main switchboard would be 230 - 32.25 = 197.75V.

Edited August 3, 2010 by electau

[elkangorito]

I see no mention of copper or aluminium conductors in Konwan's explanation. Which type of conductor is currently being used?

My equation:-

For Aluminium: Resultant voltage=V-(((0.028633*(1.004^(T-20)))*(L*2)/S)*(P/V))

For Copper: Resultant voltage=V-(((0.0180909096*(1.004^(T-20)))*(L*2)/S)*(P/V))

Does the above equation mean that 'T' equals the ambient temperature minus the 20 degress Celsius or does it mean that the ambient is 20 degrees Celsius?

[Khonwan]

I wrote (offline) and wanted to post this early yesterday but damaged my mobile-come-modem in the rain and had difficulty connecting to the Internet.

Electau, it is worse since my electrodes are aluminium. I did not specifically state that before since I have never heard of anyone (certainly not PEA) using copper in overhead power cables of anything like this length, for reasons both of cost and weight (though I know large copper cables are available).

What ambient temperature have you assumed? My equation is based on aluminium resistance of 0.028633 Ohms per mm² per metre and for copper, 0.0180909096 Ohms per mm² per metre at 20°C, increased by 4% per additional 1°C.

Elkangorito, I believe this addresses your questions. For clarity, the figures of 0.028633 and 0.0180909096 Ohms/mm²/metre for aluminium and copper respectively relate to an ambient temperature of 20°C; my equation takes account of the actual ambient temperature by increasing these figures by 4% per each additional 1°C.

Regds

Khonwan

[electau]

I wrote (offline) and wanted to post this early yesterday but damaged my mobile-come-modem in the rain and had difficulty connecting to the Internet.

Electau, it is worse since my electrodes are aluminium. I did not specifically state that before since I have never heard of anyone (certainly not PEA) using copper in overhead power cables of anything like this length, for reasons both of cost and weight (though I know large copper cables are available).

What ambient temperature have you assumed? My equation is based on aluminium resistance of 0.028633 Ohms per mm² per metre and for copper, 0.0180909096 Ohms per mm² per metre at 20°C, increased by 4% per additional 1°C.

Elkangorito, I believe this addresses your questions. For clarity, the figures of 0.028633 and 0.0180909096 Ohms/mm²/metre for aluminium and copper respectively relate to an ambient temperature of 20°C; my equation takes account of the actual ambient temperature by increasing these figures by 4% per each additional 1°C.

Regds

Khonwan

If 50sqmm Aluminium is used the resistance per km (1000m) is 0.70ohms at a temperature of 45C.

Values of resistance are based on an ambient temperature of 45C.

What are the 25sqmm cables, copper or aluminium?

[Khonwan]

Elkangorito, correction to my typo: ”increasing these figures by 4%” should read 0.4% as per equation.

Electau, 25mm² aluminium.

[electau]

Khonwan.

AC resistance at 50Hz for single core cables per kilometre.

Aluminium. 25sqmm is 1.32 ohms @ 45C. 50sqmm is 0.706 @ 45C.

Single phase voltage drop in mV/A/M is.

25sqmm is 1.617 mV for copper, 2.65 mV for aluminium at 45C

50sqmm is 0.924 mV for copper, 1.42 mV for aluminium at 45C.

Eg: 0.924* 25* 1500 = 34650mV = 34.650V.

1.42* 25* 1500 = 53250mV = 53.250V.

[Khonwan]

Electau, thank you.