agricultural tt earth

Simon-0116 · May 18, 2014

Just been to look at a job subing to grain drying firm to help then installing cables, lighting etc. The mains is 3ph in house, across newly tarmac to a small out house were it goes to db, then off to variouse sub dbs. The main swa from house is 16mm 4 core, swa as earth. ( No 300 / 500ma main switch in house.) From here it will run to the main board to the new grain shed. There electrican says put 300ma main switch on db in grain store and make it to tt, (as they havent priced to altet anything) But I thought it should be a source. So I proposed making main swa in to tt system / eart rod / 300 ma, then all of farm protected and wont trip the current farm house. Ah this is a arable farm, no livestock ever present, am I right or totally wrong and should keep my thoughts to my self

Rockingit · May 18, 2014

What is the original earthing arrangement anyway? You don't say!

Engineer54 · May 18, 2014

Why would you make a grain house TT?? I can understand where livestock is involved.

Simon-0116 · May 18, 2014

Tnc, just ever one goes on about every farm should be tt, and with there not been a dedicated earth core

Rockingit · May 18, 2014

Without knowing an overall design it's impossible to be sure, but from what you've described I would keep the TNS throughout (double check your earth conductor requirements using the adiabatic, but I'd have thought a 16mm SWA would be sufficient csa eq.) and just look at fitting RCD protection at 300 or 500mA only to locations where they may be risk of fire (think about dust etc). If the design has been done properly and discrimination taken into account then there shouldn't be any tripping issues anyway.

However........I suspect that it's probably like any other farm I've ever been on and is a real spider-web mess of DIY electrics and broken kit!!

davesparks · May 18, 2014

Simon-0116 said:
Tnc, just ever one goes on about every farm should be tt, and with there not been a dedicated earth core

Read the regs book and guidance note, don't just go by what you have heard or think everyone else does.

GLENNSPARK · May 18, 2014

Engineer54 said:
Why would you make a grain house TT?? I can understand where livestock is involved.

here...some livestock:

keep the mice down....

you`l need to construct a faraday cage for it...

JD6400 · May 18, 2014

You do not have to go TT as no livestock will ever be about ( As long as you are absolutely positive of this ! ) , but you will need to protect everything with a RCD of no greater than 300mA ( Used to be 500mA for he 17th , but has now changed to this for the 16th ) , you could even drop this to 100mA , but as most grain handling systems are now starting to go inverter drive you may have issues with just 100mA of fault protection , and don't forget it wants to be an s-type .
As for placing it at source , in the house , or at the first shed , only you know the site conditions .

Engineer54 · May 18, 2014

Simon-0116 said:
The main swa from house is 16mm 4 core, swa as earth.

Nope, using the SWA for your main earth to this grain shed is a non starter, the Armouring will not comply where main bonding is also required, it's only suitable for purposes of providing the cables CPC.... You're going to need to provide a separate earth conductor, 10mm minimum.

atm84 · May 18, 2014

What's the equivalent csa of armouring on a 16mm2 4 core??

Richard Burns · May 18, 2014

atm84 said:
What's the equivalent csa of armouring on a 16mm2 4 core??

16mm² 4 core SWA would have a csa of 50mm² steel but you would need 80mm² steel to comply with bonding requirements.

Engineer54 · May 18, 2014

atm84 said:
What's the equivalent csa of armouring on a 16mm2 4 core??

In terms of copper equivalent, nowhere near what is required!! Steel needs to be approx 8.5 X that of copper....

GLENNSPARK · May 18, 2014

here:

View attachment pvc_xlpe.pdf

Engineer54 · May 18, 2014

GLENNSPARK said:
here:

View attachment 24721

For gods sake Glenn, dump that bloody old table where it belongs, in the bloody BIN!! lol!!

GLENNSPARK · May 18, 2014

Engineer54 said:
For gods sake Glenn, dump that bloody old table where it belongs, in the bloody BIN!! lol!!

hmm...

sorry about that..lol..:sad_smile:

GLENNSPARK · May 18, 2014

i`l have a look round for an up to date one......

if someone has a link ...that`l save me a bit of effort....

Engineer54 · May 18, 2014

16mm 4 core is actually 49mm not 50mm, but the 50mm is as near as dam it!! lol!!

Table for 90[SUP]0[/SUP]C Thermosetting SWA cables operating at 70[SUP]0[/SUP]C.

Conductor CSA	Minimum CSA of SWA to meet 54G	CSA of armour 2 core	CSA of armour 3 core	CSA of armour 4 core
1.5	3.4	16	17	18
2.5	5.7	17	19	20
4	9.0	19	21	23
6	13.6	22	23	36
10	22.6	26	39	43
16	36.1	41	44	49
25	36.1	42	62	70
35	36.1	62	70	80
50	56.4	68	78	90
70	79.0	80	90	131
95	107.2	113	128	147
120	135.3	(125)	141	206
150	169.2	(138)	201	230
185	208.6	(191)	220	255
240	270.6	(215)	(250)	289
300	338.3	(235)	(269)	(319)
400	451.0	(265)	(304)	452

Engineer54 · May 18, 2014

Here you go Glenn....

Blue = min CSA of cables SWA to comply.

(Red) = Cable does not comply.

Table for 70[SUP]0[/SUP]C Thermoplastic PVC SWA cables.

Conductor CSA	Minimum CSA of SWA to meet 54G	CSA of armour 2 core	CSA of armour 3 core	CSA of armour 4 core
1.5	3.4	15	16	17
2.5	5.7	17	19	20
4	9.0	21	23	35
6	13.6	24	36	40
10	22.6	41	44	49
16	36.1	46	50	72
25	36.1	60	66	76
35	36.1	66	74	84
50	56.4	74	84	122
70	79.0	84	119	138
95	107.2	122	138	160
120	135.3	(131)	150	220
150	169.2	(144)	211	240
185	208.6	(201)	230	265
240	270.6	(225)	(260)	299
300	338.3	(250)	(289)	(333)
400	403.9	(279)	(319)	467

Table for 90[SUP]0[/SUP]C Thermosetting SWA cables operating at 70[SUP]0[/SUP]C.

Conductor CSA	Minimum CSA of SWA to meet 54G	CSA of armour 2 core	CSA of armour 3 core	CSA of armour 4 core
1.5	3.4	16	17	18
2.5	5.7	17	19	20
4	9.0	19	21	23
6	13.6	22	23	36
10	22.6	26	39	43
16	36.1	41	44	49
25	36.1	42	62	70
35	36.1	62	70	80
50	56.4	68	78	90
70	79.0	80	90	131
95	107.2	113	128	147
120	135.3	(125)	141	206
150	169.2	(138)	201	230
185	208.6	(191)	220	255
240	270.6	(215)	(250)	289
300	338.3	(235)	(269)	(319)
400	451.0	(265)	(304)	452

For CPC purposes ''ONLY''. Do not use where BONDING is also a requirement....

GLENNSPARK · May 18, 2014

Engineer54 said:
Here you go Glenn....

Blue = min CSA of cables SWA to comply.

(Red) = Cable does not comply.

Table for 70[SUP]0[/SUP]C Thermoplastic PVC SWA cables.

Conductor CSA

Minimum CSA of SWA to meet 54G

CSA of armour 2 core

CSA of armour 3 core

CSA of armour 4 core

1.5

3.4

15

16

17

2.5

5.7

17

19

20

4

9.0

21

23

35

6

13.6

24

36

40

10

22.6

41

44

49

16

36.1

46

50

72

25

36.1

60

66

76

35

36.1

66

74

84

50

56.4

74

84

122

70

79.0

84

119

138

95

107.2

122

138

160

120

135.3

(131)

150

220

150

169.2

(144)

211

240

185

208.6

(201)

230

265

240

270.6

(225)

(260)

299

300

338.3

(250)

(289)

(333)

400

403.9

(279)

(319)

467

Table for 90[SUP]0[/SUP]C Thermosetting SWA cables operating at 70[SUP]0[/SUP]C.

Conductor CSA

Minimum CSA of SWA to meet 54G

CSA of armour 2 core

CSA of armour 3 core

CSA of armour 4 core

1.5

3.4

16

17

18

2.5

5.7

17

19

20

4

9.0

19

21

23

6

13.6

22

23

36

10

22.6

26

39

43

16

36.1

41

44

49

25

36.1

42

62

70

35

36.1

62

70

80

50

56.4

68

78

90

70

79.0

80

90

131

95

107.2

113

128

147

120

135.3

(125)

141

206

150

169.2

(138)

201

230

185

208.6

(191)

220

255

240

270.6

(215)

(250)

289

300

338.3

(235)

(269)

(319)

400

451.0

(265)

(304)

452

Ta..

here...:

have your self a likes n thanks...

Knobhead · May 18, 2014

I won’t bother e-mailing stuff to you in future Glenn, you don’t look at it.
You’ve had that table for well over a year.

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