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monkey spanners
29-10-2012, 10:51 PM
Got a scroll unit i'm fitting, its 5.5hp 1ph :eek:

MRA is 37A plus 2-3A for fans, factory wiring is in 4mm and they've used a terminal strip (30A?) for it too.

Is 4mm big enough or does it all want changing (have got some 57A rated din rail to replace terminal strip on order)

I'm doing all my power in 10mm as its on a 50 breaker.

install monkey
29-10-2012, 11:02 PM
Phase
Single Phase


Power
9.2kW / 40A


Length
10m


Core Size
4mm


Voltage Drop
4.8volts based on a 10 mtr run

Phase
Single Phase


Power
9.2kW / 40A


Length
30m


Core Size
10mm


Voltage Drop
5.64volts


based on a 30 mtr run











http://www.tlc-direct.co.uk/Information/Information%20Assets/Nav%20lines%20logo%20line.gif



Cables, conduits and trunking





4.1 - Cable insulation materials (http://www.tlc-direct.co.uk/Book/4.1.1.htm)
4.4 - Cable supports, joints and terminations (http://www.tlc-direct.co.uk/Book/4.4.1.htm)




4.2 - Cables (http://www.tlc-direct.co.uk/Book/4.2.1.htm)
4.5 - Cable enclosures (http://www.tlc-direct.co.uk/Book/4.5.1.htm)




4.3 - Cable choice
4.6 - Conductor and cable identification (http://www.tlc-direct.co.uk/Book/4.6.1.htm)





















------------------------------------------------------------------


4.3.1 - Cable types (http://www.tlc-direct.co.uk/Book/4.3.1.htm)
4.3.8 - Protection by semi-enclosed (rewirable) fuses (http://www.tlc-direct.co.uk/Book/4.3.8.htm)


4.3.2 - Current carrying capacity of conductors (http://www.tlc-direct.co.uk/Book/4.3.2.htm)
4.3.9 - Cable rating calculation


4.3.3 - Methods of cable installation (http://www.tlc-direct.co.uk/Book/4.3.3.htm)
4.3.10 - Special formulas - grouping factor calculation (http://www.tlc-direct.co.uk/Book/4.3.10.htm)


4.3.4 - Ambient temperature correction factors (http://www.tlc-direct.co.uk/Book/4.3.4.htm)
4.3.11 - Cable volt drop (http://www.tlc-direct.co.uk/Book/4.3.11.htm)


4.3.5 - Cable grouping correction factors (http://www.tlc-direct.co.uk/Book/4.3.5.htm)
4.3.12 - Harmonic currents and neutral conductors (http://www.tlc-direct.co.uk/Book/4.3.12.htm)


4.3.6 - Thermal insulation correction factors (http://www.tlc-direct.co.uk/Book/4.3.6.htm)
4.3.13 - Low smoke-emitting cables (http://www.tlc-direct.co.uk/Book/4.3.13.htm)


4.3.7 - When a number of correction
--------- factors applies (http://www.tlc-direct.co.uk/Book/4.3.7.htm)
4.3.14 - The effects of animals, insects and plants (http://www.tlc-direct.co.uk/Book/4.3.14.htm)





4.3.9 - Cable rating calculationThe Regulations indicate the following symbols for use when selecting cables:


Iz

is the current carrying capacity of the cable in the situation where it is installed



It

is the tabulated current for a single circuit at an ambient temperature of 30C



Ib

is the design current, the actual current to be carried by the cable



In

is the rating of the protecting fuse or circuit breaker



I2

is the operating current for the fuse or circuit breaker (the current at which the fuse blows or the circuit breaker opens)



Ca

is the correction factor for ambient temperature



Cg

is the correction factor for grouping



Ci

is the correction factor for thermal insulation.


The correction factor for protection by a semi-enclosed (rewirable) fuse is not given a symbol but has a fixed value of 0.725.
Under all circumstances, the cable current carrying capacity must be equal to or greater than the circuit design current and the rating of the fuse or circuit breaker must be at least as big as the circuit design current. These requirements are common sense, because otherwise the cable would be overloaded or the fuse would blow when the load is switched an.
To ensure correct protection from overload, it is important that the protective device operating current (I2) is not bigger than 1.45 times the current carrying capacity of the cable (Iz). Additionally, the rating of the fuse or circuit breaker (In) must not be greater than the the cable current carrying capacity (Iz) It is important to appreciate that the operating current of a protective device is always larger than its rated value. In the case of a back-up fuse, which is not intended to provide overload protection, neither of these requirements applies.
To select a cable for a particular application, take the following steps: (note that to save time it may be better first to ensure that the expected cable for the required length of circuit will] not result in the maximum permitted volt drop being exceeded {4.3.11}). (http://www.tlc-direct.co.uk/Book/4.3.11.htm)
1. - Calculate the expected (design) current in the circuit (Ib)
2. - Choose the type and rating of protective device (fuse or circuit breaker) to be used (In)
3. - Divide the protective device rated current by the ambient temperature
----- correction factor (Ca) if ambient temperature differs from 30C
4. - Further divide by the grouping correction factor (Cg)
5. - Divide again by the thermal insulation correction factor (CI)
6. - Divide by the semi-enclosed fuse factor of 0.725 where applicable
7. - The result is the rated current of the cable required, which must be chosen
----- from the appropriate tables {4.6 to 4.9}. (http://www.tlc-direct.co.uk/Figures/Tables.htm)
Observe that one should divide by the correction factors, whilst in the previous subsection we were multiplying them. The difference is that here we start with the design current of the circuit and adjust it to take account of factors which will derate the cable. Thus, the current carrying capacity of the cable will be equal to or greater than the design current. In {4.3.7} (http://www.tlc-direct.co.uk/Book/4.3.7.htm) we were calculating by how much the current carrying capacity was reduced due to application of correction factors.
{Tables 4.6 to 4.9} (http://www.tlc-direct.co.uk/Figures/Tables.htm) give current ratings and volt drops for some of the more commonly used cables and sizes. The Tables assume that the conductors and the insulation are operating at their maximum rated temperatures. They are extracted from the Regulations Tables shown in square brackets e.g. [4D1A]
The examples below will illustrate the calculations, but do not take account of volt drop requirements (see {4.3.11}). (http://www.tlc-direct.co.uk/Book/4.3.11.htm)
Example 4.1
An immersion heater rated at 240 V, 3 kW is to be installed using twin with protective conductor p.v.c. insulated and sheathed cable. The circuit will be fed from a 15 A miniature circuit breaker type 2, and will be run for much of its 14 m length in a roof space which is thermally insulated with glass fibre. The roof space temperature is expected to rise to 50C in summer, and where it leaves the consumer unit and passes through a 50 mm insulation-filled cavity, the cable will be bunched with seven others. Calculate the cross-sectional area of the required cable.
First calculate the design current Ib


Ib=

P


= 3000A =

12.5A




-U


240





The ambient temperature correction factor is found from {Table 4.3} (http://www.tlc-direct.co.uk/Figures/Tab4.3.htm) to be 0.71. The group correction factor is found from {Table 4.4} (http://www.tlc-direct.co.uk/Figures/Tab4.4.htm) as 0.52. (The circuit in question is bunched with seven others, making eight in all).
The thermal insulation correction factor is already taken into account in the current rating table (4D2A ref. method 4] and need not be further considered. This is because we can assume that the cable in the roof space is in contact with the glass fibre but not enclosed by it. What we must consider is the point where the bunched cables pass through the insulated cavity. From {Table 4.5} (http://www.tlc-direct.co.uk/Figures/Tab4.5.htm) we have a factor of 0.89.
The correction factors must now be considered to see if more than one of them applies to the same part of the cable. The only place where this happens is in the insulated cavity behind the consumer unit. Factors of 0.52 (Cg) and 0.89 (CI) apply. The combined value of these (0.463), which is lower than the ambient temperature correction factor of 0.71, and will thus be the figure to be applied. Hence the required current rating is calculated:-


Table 4.6 - Current ratings and volt drops for unsheathed single core p.v.c. insulated cables



Cross sectional area


In conduit in thermal insulation


In conduit in thermal insulation


In conduit on wall


In conduit on wall


Clipped direct


Clipped direct


Volt drop


Volt drop




(mm)


(A)


(A)


(A)


(A)


(A)


(A)


(mV/A/m)


(mV/A/m)




-


2 cables


3 or 4 cables


2 cables


3 or 4 cables


2 cables


3 or 4 cables


2 cables


3 or 4 cables




1.0


11.0


10.5


13.5


12.0


15.5


14.0


44.0


38.0




1.5


14.5


13.5


17.5


15.5


20.0


18.0


29.0


25.0




2.5


19.5


18.0


24.0


21.0


27.0


25.0


18..0


15.0




4.0


26.0


24.0


32.0


28.0


37.0


33.0


11.0


9.5




6.0


34.0


31.0


41.0


36.0


47.0


43.0


7.3


6.4




10.0


46.0


42.0


57.0


50.0


65.0


59.0


4.4


3.8




16.0


61.0


56.0


76.0


68.0


87.0


79.0


2.8


2.4







Table 4.7 - Current ratings and volt drops for sheathed multi-core p.v.c.-insulated cables



Cross sectional area


In conduit in thermal insulation


In conduit in thermal insulation


In conduit on wall


In conduit on wall


Clipped direct


Clipped direct


Volt drop


Volt drop




(mm)


(A)


(A)


(A)


(A)


(A)


(A)


(mV/A/m)


(mV/A/m)




-


2 core


3 or 4 core


2 core


3 or 4 core


2 core


3 or 4 core


2 core


3 or 4 core




1.0


11.0


10.0


13.0


11.5


15.0


13.5


44.0


38.0




1.5


14.0


13.0


16.5


15.0


19.5


17.5


29.0


25.0




2.5


18.5


17.5


23.0


20.0


27.0


24.0


18.0


15.0




4.0


25.0


23.0


30.0


27.0


36.0


32.0


11.0


9.5




6.0


32.0


29.0


38.0


34.0


46.0


41.0


7.3


6.4




10.0


43.0


39.0


52.0


46.0


63.0


57.0


4.4


3.8




16.0


57.0


52.0


69.0


62.0


85.0


76.0


2.8


2.4













10mm cable is only rated at 43amp, suggest running 20 mm conduit and tri rated singles

install monkey
29-10-2012, 11:07 PM
tri rated specs 10mm 75amp 6 mm 53amp http://www.eland.co.uk/documents/Tri-rated%20Cables.pdf

mikeref
29-10-2012, 11:08 PM
Or try this Mr. Monkey..
http://www.google.com.au/url?sa=t&rct=j&q=4mm2%20cable%20rating&source=web&cd=2&cad=rja&sqi=2&ved=0CCYQFjAB&url=http%3A%2F%2Fjaw.iinet.net.au%2Fstuff%2Fcablecalc.html&ei=AwuPUNnGNMyziQfipIGIBA&usg=AFQjCNEWOL84iet_dfCPWpfIJqOYqzg_7g

install monkey
29-10-2012, 11:10 PM
is that to aussie specs??? poor monkeyspanners would get strung up if he ran a 2.5mm 2 core flex 35mtr to it:rolleyes:
Or try this Mr. Monkey..
http://www.google.com.au/url?sa=t&rct=j&q=4mm2%20cable%20rating&source=web&cd=2&cad=rja&sqi=2&ved=0CCYQFjAB&url=http%3A%2F%2Fjaw.iinet.net.au%2Fstuff%2Fcablecalc.html&ei=AwuPUNnGNMyziQfipIGIBA&usg=AFQjCNEWOL84iet_dfCPWpfIJqOYqzg_7g

mikeref
29-10-2012, 11:12 PM
4mm = 36 amps on 240 :p Max.. Wouldn't be game to try it though.

install monkey
29-10-2012, 11:14 PM
take it your customer doesn't want to pay for an inverter and is too tight to have a 3 phase supply, saftronics do a soft start kit for around 150 quid, reduce the inertia on start up, only 3 dials so monkeyproof:confused:

monkey spanners
29-10-2012, 11:40 PM
Thanks for the replies :)

Kit was supplied by others, i'm just installing it for them, looks like it needs to be 10mm as its off a 50A breaker.

install monkey
29-10-2012, 11:58 PM
3/8 copper pipe is good for 80 amp just wrap it in your 1 roll of insulation tape!!! haha
Thanks for the replies :)

Kit was supplied by others, i'm just installing it for them, looks like it needs to be 10mm as its off a 50A breaker.

Magoo
30-10-2012, 01:39 AM
Use a local electrician to spec the cabling size, reduce your risk.