The table below helps you select the correct gauge of wire for your loop amplifier. The type of wire is not too important, though experience has shown that a stranded cable with tri-rated insulation is probably the easiest to install and most robust in use. So for example, an ILD122 amplifier when using a 1.5mm² loop cable, will work with a minimum length down to 17m and a maximum length of up to 90m. Any length in-between these two values should work fine though beware of working right at the limits of cable size. If in doubt, use a different size of cable such that the total loop length is well within the minimum and maximum lengths.
Cable / Wire Data | ILD20 | ILD122 | ILD252 (USA) | ILD9 | |||||||
Length (m) | Length (m) | Length (m) | Length (m) | ||||||||
Wire gauge mm² |
Resistance | |Z| @ | Min | Max | Min | Max | Min | Max | Min | Max | |
Ω per | 1.6 KHz | DC | 1.6 KHz | DC | 1.6 KHz | DC | 1.6 KHz | DC | 1.6 KHz | ||
100ft | 100m | Ω/m | 0.2Ω | 1.2Ω | 0.2Ω | 2Ω | 0.3Ω | 2.72Ω | 0.4Ω | 3.75Ω | |
0.5 | 1.051 | 3.448 | 0.0399 | 6 | 29 | 6 | 50 | 9 | 68 | 12 | 94 |
0.75 | 0.701 | 2.299 | 0.0305 | 9 | 44 | 9 | 65 | 13 | 89 | 17 | 123 |
1.0 | 0.526 | 1.724 | 0.0265 | 12 | 57 | 12 | 76 | 17 | 102 | 23 | 142 |
1.5 | 0.350 | 1.149 | 0.0223 | 17 | 67 | 17 | 90 | 26 | 122 | 35 | 168 |
2.5 | 0.210 | 0.690 | 0.0194 | 29 | 77 | 29 | 103 | 44 | 140 | 58 | 194 |
4.0 | 0.131 | 0.431 | 0.0186 | X | X | 46 | 108 | 70 | 146 | 93 | 202 |
FB 1.8* | 0.292 | 0.958 | 0.0150 | 21 | 100 | 21 | 133 | 31 | 181 | 42 | 250 |
AWG wire | Ω/100ft | Length (ft) | Length (ft) | Length (ft) | Length (ft) | ||||||
22 7×30 | 1.482 | 4.861 | 1.603 | 13 | 67 | 13 | 125 | 20 | 169 | 27 | 234 |
20 7×28 | 0.933 | 3.062 | 1.117 | 21 | 107 | 21 | 179 | 32 | 243 | 43 | 336 |
18 16×30 | 0.648 | 2.127 | 0.892 | 31 | 154 | 31 | 224 | 46 | 304 | 62 | 420 |
16 26×30 | 0.399 | 1.309 | 0.706 | 50 | 251 | 50 | 283 | 75 | 384 | 100 | 531 |
14 41×30 | 0.253 | 0.830 | 0.607 | 79 | 395 | 79 | 330 | 119 | 447 | 158 | 618 |
12 65×30 | 0.160 | 0.523 | 0.574 | X | X | 125 | 348 | 188 | 472 | 251 | 653 |
10 65×28 | 0.101 | 0.330 | 0.561 | X | X | 199 | 357 | 298 | 483 | 398 | 669 |
FB 1.8* | 0.292 | 0.958 | 0.458 | 69 | 343 | 69 | 437 | 103 | 592 | 137 | 819 |
Cable / Wire Data | ILD100 | ILD300 | ILD500 | ||||||||
Length (m) | Length (m) | Length (m) | |||||||||
Wire gauge mm² |
Resistance | |Z| @ | Min | Max | Min | Max | Min | Max | |||
Ω per | 1.6 KHz | DC | 1.6 KHz | DC | 1.6 KHz | DC | 1.6 KHz | ||||
100ft | 100m | Ω/m | 0.2Ω | 1.0Ω | 0.2Ω | 1.3Ω | 0.3Ω | 2.0Ω | |||
0.5 | 1.051 | 3.448 | 0.0399 | 6 | 23 | 6 | 33 | 9 | 55 | ||
0.75 | 0.701 | 2.299 | 0.0305 | 9 | 29 | 9 | 43 | 13 | 72 | ||
1.0 | 0.526 | 1.724 | 0.0265 | 12 | 34 | 12 | 49 | 17 | 83 | ||
1.5 | 0.350 | 1.149 | 0.0223 | 17 | 40 | 17 | 58 | 26 | 99 | ||
2.5 | 0.210 | 0.690 | 0.0194 | 29 | 46 | 29 | 67 | 44 | 114 | ||
4.0 | 0.131 | 0.431 | 0.0186 | X | X | 46 | 70 | 70 | 118 | ||
FB 1.8* | 0.292 | 0.958 | 0.0150 | 21 | 60 | 21 | 87 | 31 | 147 | ||
AWG wire | Ω/100ft | Length (ft) | Length (ft) | Length (ft) | |||||||
22 7×30 | 1.482 | 4.861 | 1.603 | 13 | 54 | 13 | 81 | 20 | 135 | ||
20 7×28 | 0.933 | 3.062 | 1.117 | 21 | 81 | 21 | 116 | 32 | 197 | ||
18 16×30 | 0.648 | 2.127 | 0.892 | 31 | 101 | 31 | 146 | 46 | 247 | ||
16 26×30 | 0.399 | 1.309 | 0.706 | 50 | 128 | 50 | 184 | 75 | 312 | ||
14 41×30 | 0.253 | 0.830 | 0.607 | 79 | 148 | 79 | 214 | 119 | 363 | ||
12 65×30 | 0.160 | 0.523 | 0.574 | X | X | 125 | 226 | 188 | 383 | ||
10 65×28 | 0.101 | 0.330 | 0.561 | X | X | 199 | 232 | 298 | 392 | ||
FB 1.8* | 0.292 | 0.958 | 0.458 | 69 | 197 | 69 | 284 | 103 | 481 |
* FB 1.8 is Flat Copper Tape
Table Notes
The table above gives comprehensive information on the minimum and maximum length of cable of a particular wire gauge that can be used with specific Ampetronic loop drivers. Each driver has a specified minimum resistance and maximum impedance at 1.6KHz which can be driven at full current.
Feeder Cable
The values given in the table ignore the resistance of the feeder cable (the cable connecting the loop to the loop driver) which is normally very low. If the situation is marginal, or where very long feeder cables are involved, additional design must be done to compensate. Feeder cable should always be tightly twisted to ensure that the reactive component is very low resulting in a low magnetic field near to the equipment. Use of shielded cable has no real advantages as magnetic radiation is not affected. Parallel wire cable (eg Fig 8) as used by some loudspeaker manufacturers is not recommended. Very often, the wire gauge of the feeder will be similar to the actual loop cable.
The actual feeder length is double the physical length for resistance (send and return). This is important when calculating the total resistance of the system.
Star Quad Feeder Cables
For very long feeder cables, the recommendation is to use a 4-core round cable in a “star quad” configuration. Optimum cable size is 1.5mm² / 2.5mm² (14AWG / 16AWG). The opposing cores are connected together, providing a very low resistance and inductance with little magnetic radiation. This style of cable is often used for 3-phase + earth power connection of machinery.
UK style is 3184Y, harmonised H05VV-F. Similar UL approved cable is SV-3, UL recognised 4097. Total resistance of 100m of 3184Y cable, 2.5mm² per core is 0.69Ω (4-core 14AWG cable is 0.252Ω/100ft). This is well inside the capabilities of the Ampetronic loop drivers.