What's the wire length limit on a Honeywell VISTA's polling loop?

The Vista-128BPT and 250BPT have flexible wire length limits outlined in the charts below, based on current draw and wire gauge, and whether or not the wire is shielded. A 2-wire polling loop provides both current (128mA) and data. Common rules regarding the polling loop are listed below.

  • Unshielded wire is preferable to shielded wire (wire in a metal conduit). If shielded wire is used, be sure to ground one end of the shield. The user should know that using shielded wire cuts the available wire distance in half. This is due to the capacitive effect of the shield or conduit. This is not an issue with non-metal conduit.
  • Polling loop wire should be kept at least 6 inches from keypad wiring, heavy electrical wiring, fluorescent lighting, phone or intercom wiring, or any other source of noise that might disrupt the polling loop. If the user must install near a source of noise, then use shielded wire, or metal conduit, and accept the lower distances supported.
  • Always observe proper polarity when connecting devices to the polling loop. Reversed polarity will behave like a short, and can cause a trouble condition on every device connected to the polling loop.
  • If a device has the option of using dip switch settings, or serial number settings, it MUST use serial number on the Vista-128BPT and Vista-250BPT.
  • If longer wire or additional current is needed, a 4297 polling loop extender can be used. In addition to providing another 128mA of current, the 4297 also acts as a short isolator, keeping any short on the outgoing loop isolated from other loop segments. Multiple 4297s can be used. See the charts below to determine the acceptable wire distance for a polling loop run based on the gauge wire used, and amount of current being drawn on the run. Note that there is a separate chart for unshielded vs. shielded wire.
Table: Unshielded (or non-metal conduit)
Total Load
(mA @ 11.5) Vdc
22 ga 20 ga 18 ga 16 ga
1-4 12,000 12,000 12,000 12,000
5-8 12,000 12,000 12,000 12,000
9-16 7,270 11,710 12,000 12,000
17-24 4,850 7,810 12,000 12,000
24-32 3,640 5,850 9,260 12,000
33-40 2,910 4,680 7,410 11,760
41-48 2,420 3,900 6,170 9,800
49-56 2,080 3,350 5,290 8,400
57-64 1,820 2,930 4,630 7,350
65-72 1,620 2,600 4,110 6,540
73-80 1,450 2,340 3,700 5,880
81-88 1,320 2,130 3,370 5,350
89-96 1,210 1,950 3,090 4,900
197-104 1,120 1,800 2,850 4,520
105-112 1,040 1,670 2,650 4,200
113-120 970 1,560 2,470 3,920
121-128 910 1,460 2,310 3,680


Table: Shielded (or metal conduit)
Total Load
(mA @ 11.5) Vdc
22 ga 20 ga 18 ga 16 ga
1-4 6,000 6,000 6,000 6,000
5-8 6,000 6,000 6,000 6,000
9-16 6,000 6,000 6,000 6,000
17-24 4,850 6,000 6,000 6,000
24-32 3,640 5,850 6,000 6,000
33-40 2,910 4,680 6,000 6,000
41-48 2,420 3,900 6,000 6,000
49-56 2,080 3,350 5,290 6,000
57-64 1,820 2,930 4,630 6,000
65-72 1,620 2,600 4,110 6,000
73-80 1,450 2,340 3,700 5,880
81-88 1,320 2,130 3,370 5,350
89-96 1,210 1,950 3,090 4,900
197-104 1,120 1,800 2,850 4,520
105-112 1,040 1,670 2,650 4,200
113-120 970 1,560 2,470 3,920
121-128 910 1,460 2,310 3,680

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