Direct answer

How many devices fit on a Hochiki ESP loop depends on loop current, not just a fixed device count. An ESP loop has 127 main addresses (1 to 127); on panels that support base sounder addressing, such as Latitude, base sounders fitted under sensors use the addresses 128 to 254. Add up the quiescent and alarm current of every device and keep both within 80% of the loop current rating in the panel manual (500 mA per loop on Latitude). The Hochiki Loop Calculator, available from Technical Support, does this calculation.

Applies to

Products / Models: Hochiki ESP addressable loops on Latitude panels and on compatible third-party panels: ESP sensors, manual call points, CHQ modules, YBO-BS / YBO-BSB2 base sounders, CHQ-WS2 / CHQ-WSB2 wall sounders, VADs and beacons, and loop-powered beam detectors; Hochiki Loop Calculator
Firmware / Version: All versions. Check the Loop Calculator version under Help > About.
Region: UK / Europe
Standards: BS 5839-1:2025 (standby power supply); Latitude panels — EN 54-2, EN 54-4, EN 54-13

Steps: check loop loading with the Loop Calculator

List every device on the loop
- Include detectors, manual call points, isolator bases, modules, wall sounders, base sounders, beacons, VADs and any loop-powered beam detectors. Do not size a loop on sounders alone; every device adds to the loop current.
- Enter the quantities for each loop and each panel separately, not the total for the whole site.
Select the exact panel model
- The calculator judges the result against the limits held for the selected panel, so the same devices can give a different result, or a different warning colour, when another panel is selected.
- For a third-party panel, confirm the loop current rating and any design margin with the panel manufacturer.
Put each device in the correct address column
- Sensors, manual call points, modules and sounders used on their own as wall sounders go in the 1 to 127 column.
- Base sounders and base sounder beacons fitted under a sensor go in the 128 to 254 column. The panel normally gives a base sounder the address of the sensor fitted to it plus 127, so it does not use a main address. Addresses above 127 may not be visible at the panel, depending on how the panel manufacturer implements them.
Enter the sounder and visual alarm settings you will use
- Enter the sound level (dB) and other settings that will be programmed on site. A sounder draws more current in alarm at a higher sound level, and VADs can draw considerably more current than open beacons, so the alarm current depends on these settings as well as on the device count.
Set the device distribution
- Set the distribution to even when the devices are spread evenly along the loop cable. Adjust it when there is a long cable run before the first device. Cable length and load cause voltage drop, which must not take the supply below the minimum operating voltage of the devices.
Check the quiescent current and the alarm current
- Both results must stay within the loop current rating stated in the panel manual. On Latitude panels each loop is rated at 500 mA.
- Leave spare capacity on each loop for future additions. Hochiki Europe recommends designing a new loop so that no more than 80% of the available loop capacity is used, to allow for future requirements. On a loop rated at 500 mA, this means a calculated load of no more than about 400 mA. If the panel manufacturer specifies a lower limit, use that limit.
- The loop current is not always shown on the panel display. Calculate it from the system configuration, and confirm it by measurement during commissioning. A current figure on a data sheet applies under the conditions stated on that data sheet; if a figure does not match what you expect, measure the current of one device on site.
Rebalance the design if a loop is over the limit
- Move devices to a less heavily loaded loop or to another panel, so that no loop is much more heavily loaded than the others.
- Move alarm loads off the loop where the design allows, for example to the panel sounder circuits or to conventional sounder circuits driven by a CHQ-DSC2(SCI), which takes its sounder power from an auxiliary 24 V DC supply. Which Hochiki CHQ modules need an external 24 V PSU? explains which modules run on loop power only and which need an auxiliary supply.
- Do not apply a fixed number to loop-powered beam detectors or loop-powered VADs. Decide the quantity by calculation, and check every current listed on the data sheet for the exact model, including any start-up or commissioning current.
Size the standby batteries from the same figures
- The required standby period depends on the system category and the premises; it is not 72 hours for every system. BS 5839-1:2025 gives the method for calculating standby battery capacity in Annex E. Use the battery calculation in the panel manual. The Latitude battery tables are for guidance only, and the required capacity should be calculated from the currents measured during commissioning.
- If devices are added to an existing system, check that the power supply rating and the standby battery capacity are still adequate for the new load.

If the Loop Calculator result looks wrong

If the device count is about double what you entered, check whether base sounders have been entered in the 1 to 127 column. Move them to the 128 to 254 column.
If the result changes colour when you select a different panel, this is expected, because each panel has its own limits. Check that the selected panel is the one on site.
If a panel manufacturer's configuration software shows a different current for the same loop, remember that different tools can use different device current values and assumptions. Do not design to the lower figure until the difference has been explained. Confirm the loop current by measurement during commissioning, and contact the panel manufacturer and Hochiki Europe Technical Support.

When to contact technical support

You need the Hochiki Loop Calculator or want to confirm that you have the current version.
The Loop Calculator does not install, start or display correctly on your computer.
The calculator result still looks wrong after the address columns and the panel selection have been checked.
A loop is close to its limit and the design includes loop-powered VADs, beacons or beam detectors.
The measured loop current differs noticeably from the calculated value.
You need the loop current rating or design margin of a third-party panel. Contact the panel manufacturer for the panel limits, and Hochiki Europe Technical Support for Hochiki device data.

Safety note

This article is general guidance for Hochiki Europe products. Design, installation, commissioning, maintenance and modification of fire detection and alarm systems should be carried out by, or under the responsibility of, a competent person in accordance with the applicable standards (for example BS 5839-1 in the UK). Statutory requirements imposed by the relevant enforcing authority also apply. Always refer to the current product manual and data sheet for the exact model before carrying out any work.

References

Last reviewed: 2026-10-27 — Reviewed by: Hochiki Europe Technical Support

How many devices can I put on a Hochiki ESP loop?

Loop capacity is set by the quiescent and alarm current against the panel's loop current rating, with spare capacity, not by a fixed device count alone.