2026-11-1111 min read

Auxiliary Contacts, Motor Kits and Add-on Poles: Specifying Switch Disconnector Accessories

Auxiliary contacts, motor kits, neutral and add-on poles turn a switch disconnector into part of a control system. How to specify them so they fit the frame.

A switch disconnector on its own is a mechanical device with one job: make, carry and break current, and isolate the circuit when it is open. On a modern industrial board it is rarely left on its own. Somebody needs to know whether it is open or closed. Somebody wants to operate it from a control room or from a transfer controller. Somebody needs a fourth pole that was not on the original drawing.

That is what the accessory range is for — auxiliary contacts, motor kits, add-on and neutral poles, and bridging links. They are small line items on an order, and like the handles and shafts that operate the same switches, they are frame-specific. An auxiliary contact for one series will not fit another, and a motor kit is sized to a particular frame and current band.

This article covers what each accessory does, where it earns its place, what the relevant standards say, and a checklist you can paste into an enquiry so the accessories arrive matched to the switch.

Why accessories are specified with the switch, not after it

The common failure is sequencing. The switch disconnector is selected early — on current rating, poles and breaking duty, as described in our guide to choosing between a switch disconnector, circuit breaker or isolator. The control requirements arrive later, from a different discipline: the controls engineer wants position feedback into a PLC, the client's operations team wants remote operation, the earthing design changes and the neutral now has to be switched.

By then the switch is on order or installed, and the question becomes whether the accessory exists for that exact frame and whether there is physical room to fit it. Sometimes the answer is yes. Sometimes it means a different switch.

Specifying the accessories at the same time as the switch avoids that. It also makes the quotation honest: the price and lead time of a motorised changeover is not the price of the changeover switch.

Auxiliary contacts: telling the rest of the system what the switch is doing

An auxiliary contact is a small, low-current switching element mechanically coupled to the main switch. When the main contacts open or close, the auxiliary contact changes state with them. It carries no load current — it carries a signal.

What they are used for

Position indication. An indicator lamp on the panel door, or a status point in a SCADA or building management system, showing whether a feeder isolator is open or closed.
Interlocking. Preventing one device from closing while another is closed — for example, ensuring a generator breaker cannot be commanded closed while the utility incomer is in circuit, as part of the interlocking discussed in manual vs automatic changeover switches.
Control logic. Telling a PLC or a transfer controller that a switch has actually moved, rather than assuming it moved because a command was sent.
Safe-isolation confirmation. Giving a control system a hard signal that the isolation point is open, which supports — but never replaces — the physical lockout described in our article on lockout/tagout locking devices.

NO, NC and why you usually want both

Auxiliary contacts are described by their contact configuration:

NO (normally open) — open when the main switch is OFF, closed when it is ON.
NC (normally closed) — closed when the main switch is OFF, open when it is ON.

A 1NO + 1NC contact block gives one of each, which is the most useful single unit for indication and interlocking: the NO drives an "ON" signal, the NC drives an "OFF" signal, and a control system that sees both (or neither) knows something is wrong — a broken wire, a failed contact, or a switch stuck mid-travel. A single contact cannot tell the difference between "switch open" and "signal wire cut".

That is the practical case for wiring both states back to the control system on any isolator whose position actually matters.

What the catalogue offers

GNTech's catalogue lists auxiliary contacts for several Telergon switch families, each tied to its series:

S5 switch disconnectors (40 A – 6300 A): auxiliary contacts listed under catalogue ids 254 and 255, SKUs D5LAU01 / DS-AU11 and D5LAU02 / DS-AU12.
S3 compact switch disconnectors (16 A – 125 A): catalogue id 436, described as "Auxiliary contact, S3, 1NO+1NC reverse", with SKUs DS3AUP1, DS3AUP2, DS3AUP1R and DS3AUP2R.
CEC compact range (63 A – 125 A): catalogue id 253, SKU DCEAUB1.
M3 fuse switch disconnectors (30 A – 250 A): catalogue id 410, SKUs DM-AU11 and DM-AU12.
ZBK disconnectors: catalogue id 476, "Auxiliary contact 1N/O + 1N/C for ZBK disconnectors (incl. 8-pole)", SKU ZBKLH11.

Two practical points follow from that list. First, the auxiliary contact is chosen by switch series, not by function — the catalogue lists a separate auxiliary SKU for each series, so order the one listed for the switch you have. Quote the main switch's series and part number on the accessory line. Second, where a series offers more than one auxiliary SKU, the variants differ in contact configuration or mounting orientation; confirm which one suits the wiring scheme against the series datasheet before ordering, rather than assuming the first SKU is the one you need.

Ratings: what an auxiliary contact can switch

Auxiliary contacts are control-circuit devices, and their ratings sit under IEC 60947-5-1 (control circuit devices and switching elements), not under the IEC 60947-3 rating of the main switch. They are rated by utilization category — AC-15 for switching electromagnetic loads on AC (relay and contactor coils, solenoids) and DC-13 for the DC equivalent — at a stated voltage and current.

Two consequences:

Do not use an auxiliary contact to switch a power load. It is rated for coils and signals. If the logic needs to switch something substantial, the auxiliary drives a relay or contactor that does.
Check the DC rating if the control supply is DC. A contact comfortably rated at 230 V AC can have a much lower permitted current at 110 V or 220 V DC, because a DC arc does not extinguish at a current zero. Substation and battery-backed control supplies are often DC, so this matters more than it first appears.

The specific ratings for each contact are in the series datasheet; read them against the actual control voltage and load, not the panel's nominal supply.

Early and late contacts

Some auxiliary contacts are designed to change state before the main contacts move (early-break or early-make), so that a control circuit is warned — or a contactor is dropped out — before the main contacts open under load. Others change state with or after the main contacts. If the scheme depends on timing — for example, de-energising a contactor before an isolator is opened, so the isolator never breaks motor current — that timing must be stated in the enquiry and confirmed against the datasheet. "1NO + 1NC" alone does not describe it. The same point comes up with cam switches, where contact sequence is part of the specification rather than a detail.

Motor kits: operating the switch without a hand on the handle

A motor kit (motor operator, motorised unit) mounts on the switch and drives its operating mechanism electrically. The switch then opens and closes on a command signal — from a pushbutton, a PLC output, a SCADA command or a transfer controller.

Where motorised operation earns its cost

Automatic transfer. The most common case in South Africa. A motorised changeover switch, driven by a controller that monitors the utility supply, is the switching element of an automatic transfer scheme for a standby generator or a battery energy storage system. Transfer switching equipment of this kind falls under IEC 60947-6-1.
Remote operation of large incomers and feeders, where operating the switch from a control room keeps people out of the switchroom during switching. That has a safety benefit as well as a convenience one, and it connects directly to the arc-flash exposure reduction discussed in our arc flash safety guide.
Load management — shedding or restoring non-essential feeders on a schedule or on a signal.

What the catalogue offers

Motor kits in the catalogue are listed per switch series and per frame size, which is the point to take away: a motor kit is ordered against a specific frame.

S5 switch disconnectors: catalogue id 258, with SKUs UM-S1A230Z (size 1, 500 A), UM-S2A230Z (size 2, 800 A) and UM-S31230M (size 3, 1250 A).
S5F changeover switches (125 A – 3150 A): catalogue id 259, SKUs UM-C0A230Z (size 0, 200 A) and UM-C45230M (size 4, 2000 A).
CCF changeover switches (200 A – 1250 A): catalogue id 260, SKUs UM-C1A230Z (size 1, 400 A), UM-C2A230Z (size 2, 800 A) and UM-C31230M (size 3, 1000 A); and catalogue id 499, "Motorized unit kit, size 2, 230VAC, 500 - 630A", SKUs UM-C21230M and UM-C21230Z.

What to decide before ordering a motor kit

The frame and current band, taken from the actual switch part number. Kits are listed by frame size, so order the kit listed for your switch's size rather than the nearest current rating.
The control voltage. Id 499 is described as 230 VAC; confirm the supply voltage of every kit against its datasheet and against what is available in the panel — and, critically, against what is available when the supply has failed. A motorised changeover that needs mains to transfer to the generator has a design problem. The control supply for transfer schemes usually comes from the side that is live, or from a UPS or battery.
Manual override. Confirm that the switch can still be operated by hand, safely, if the motor or its supply fails — and how the motor is disabled while that happens.
Padlocking in the OFF or isolated position. A motorised switch that can be commanded closed remotely must also be lockable so that it cannot be, while someone is working downstream. This is the same isolation discipline covered in our lockout/tagout guide, with a remote command path added to the list of things that must be locked out.
Position feedback. A motor kit is almost always paired with auxiliary contacts so the controller can confirm the switch actually moved. Order both together.

Add-on poles and neutral poles: changing the pole count

Switch disconnectors are ordered by pole count — 3P, 3P+N and so on. Add-on and neutral poles allow that to be adjusted on some ranges.

Neutral poles

The catalogue lists neutral poles for the ZBK range: catalogue id 477 (neutral pole for 25 – 40 A, SKU ZBKN40V) and id 491 (neutral terminal, size 0, 63 – 80 A, SKU ZBKN80V).

Whether a neutral must be switched is an earthing-system decision, not a product preference. The classic case is a changeover between the utility supply and a generator where the generator has its own neutral-to-earth bond: switching the neutral as well as the phases keeps the two neutral-earth bonds from being paralleled through the installation. The decision belongs in the design, made against SANS 10142-1 and the site's earthing arrangement — our overview of electrical safety standards in South Africa covers the framework. What matters for ordering is that the decision is made before the switch is ordered, so that the right pole count, or the right neutral accessory, comes with it.

Add-on poles

The catalogue lists side-mount add-on poles for the S3 compact range: catalogue id 434, described as "Side Mount, Add-on Pole, Size 000, for S3 100-125A Front", with variants across the S3 current bands (for example DS3PSAF and DS3PSAR at 40 A, DS3PSBF at 80 A, DS3PS0F at 125 A). As with every accessory here, the add-on pole is listed against a specific series and current band, so order it against the switch it attaches to.

Bridging links

The catalogue also lists copper bridging links for the S5 range — catalogue id 406, described as "Copper bridging links for size 1 (400A switch) (2 links)", with SKUs DS-PI11, DS-PI14 (400 A) and DS-PI2D (630 A). Which connection arrangement each link suits is set out in the S5 datasheet; specify the link from there, against the size of the switch it serves.

A specification checklist for switch disconnector accessories

Paste this into an enquiry alongside the switch schedule:

Switch series and full part number for every device the accessory attaches to.
Auxiliary contacts: quantity per switch, configuration (NO / NC / 1NO+1NC), and whether early or late operation relative to the main contacts is required.
Auxiliary contact duty: control voltage, AC or DC, and the load being switched (lamp, relay coil, PLC input).
Motor kit: frame size, current band, motor control voltage, and where that control supply comes from when the main supply has failed.
Manual override and padlocking arrangements for any motorised device.
Position feedback paired with every motor kit.
Neutral switching: whether the neutral must be switched, and the earthing reasoning behind it.
Add-on poles required, by series and current band.
Bridging links required by the connection arrangement, by series and size.
Space in the enclosure for the accessories — side-mounted auxiliaries, add-on poles and motor kits all add width or depth, which needs to be in the panel layout before the enclosure is ordered.

The failures that come back

The auxiliary does not fit. Ordered by function ("1NO+1NC auxiliary") rather than by series. Quote the switch part number on the accessory line.

The indication lies. A single NO contact wired to a lamp: a broken wire shows the same as an open switch. Wire both states back where position matters, and include the auxiliary circuit in routine maintenance testing.

The contact burns out. An auxiliary used to switch a load it was never rated for, or a DC control circuit run on a contact selected for its AC rating.

The transfer will not happen. A motorised changeover whose motor supply comes from the side that has just failed. Design the control supply for the outage, not for normal operation.

The neutral was an afterthought. The earthing design changed after the switch was ordered, and the frame does not take a neutral accessory. Make the neutral decision first.

Each of these is the same mistake: treating an accessory as something to add later. When things do go wrong in service, our guide to fault-finding on industrial switchgear covers how to trace them.

Getting it right first time

Accessories are what turn a switch disconnector from a manually operated isolator into part of a control and protection system. They are inexpensive relative to the switch, but each one is tied to a specific series and frame, and the wrong one costs a return trip and a delayed commissioning date.

GNTech supplies Telergon switch disconnectors, changeover switches and fuse switches for South African industrial installations, together with the auxiliary contacts, motor kits, add-on and neutral poles listed for them, so the accessory schedule can be matched to the switch schedule at quotation. Send us the switch part numbers and the control requirements and we will return a matched accessory list. For broader selection help, start with our buyer's guide to industrial switchgear in South Africa or our switchgear sizing and load calculation guide.

Talk to us about matching accessories to your switch schedule.