Signal Tower: Base, Pole, Circuits and Voltage

The old stack on the packing line has cracked, maintenance wants a replacement fitted before the next shift, and the label on the base has worn off. A machine signal tower looks simple until you order one, because the base, pole, circuits and voltage all have to match what is already on the machine. Work through those choices in order, then add modules on top, and the order usually falls into place.

Start with the base: how the tower mounts and how the cable enters

Pick the mounting first, because everything else hangs off it. In the 70mm IP67 range, the complete towers come on an aluminium pole, while separate bases cover other layouts: an M20 tube base, a vertical-mount base with a 1/2 inch NPT entry, and surface-mount bases for fixing straight onto a flat surface.

If the tower goes onto a threaded M20 tube, look at the 25cm M20 tube base. If it has to stand off a vertical face, check the 7-circuit vertical-mount base. For an existing pole, there is a 250mm pole base adaptor. Check the datasheet to confirm how each adaptor fits your base before you order.

Cable entry is the part that catches people. The 1/2 inch NPT bases take a US-style pipe thread, while Australian conduit and glands are generally metric. Decide how the cable gets in before you order, and have the right adaptor or gland ready. The signal tower accessories, meaning the adaptors and mounting parts, are small items, but a missing one stops the install.

Pole length: get the light above whatever blocks it

A tower that sits below a guard rail or a machine hood is only seen by the person standing next to it. Walk the floor, find the furthest spot where the operator or supervisor needs to see the light, and choose a pole that clears anything in that line of sight.

The complete towers listed here come with a 40cm pole in the 24V version and a 60cm pole in the 240V 3-circuit and 7-circuit versions. If the machine needs a different height, building the tower from a base and an adaptor gives you more control.

Voltage: 24V DC or 240V AC

Check what the machine controller can actually switch. Many machine PLCs and control panels run their outputs at 24V DC, so a 24V tower like the 24V AC/DC signal tower with a 40cm pole can usually be driven straight from an output, as long as the output's current rating covers the load. A 240V AC tower makes more sense where the machine already has a mains-rated switching device, such as a relay, in the circuit.

The LED modules listed below are 24V AC/DC, so check the datasheet to confirm how module voltage relates to the 240V bases before mixing parts. Keep licensing in mind too: fixed wiring at 240V AC must be done by a licensed electrician in Australia, and the rules for extra-low voltage work can differ between states.

Circuits: 3, 7, or a simple 2-element tower

The circuit count in the product names tells you how many separate circuits the base supports. In practice, that is how many separate signals the controller can send. Count what the machine needs to say today, such as run, warning and fault, then add one spare. A line that gets a new status later will otherwise need a new base.

A 7-circuit 240V tower on a 60cm pole leaves room to grow on a busy machine. A 3-circuit tower covers a basic run, warning and fault setup, and there is a 2-element 240V tower for machines that only need to show two states.

Modules on top: what each one tells the operator

Each module sits on its own circuit, and the 70mm range comes in steady, rotating, strobing and sounder options. Which behaviour goes on each circuit, steady, flashing or strobe, is covered in our Stack Light article.

A rotating LED module gets attention fast. If you are also weighing a standalone unit, see our notes on a halogen or LED rotating beacon.

The 102dB sounder module adds an audible alert for noisy areas. It is rated IP66, while the other listed 70mm modules are IP67. The two ratings test different things, so check it suits how the machine gets cleaned. For sizing in general, see sound, voltage and IP rating.

Common mistakes when specifying a signal tower

• Choosing the pole before the mounting. It happens when pole length is the only thing left on the old label. The tower arrives, does not sit on the existing mount, and the install stops while an adaptor is sourced. Confirm the mounting type first, then the pole.
• Counting only today's lights. A machine with three states makes three circuits look right. Months later someone asks for a fourth signal and the base has nothing left. Count one spare.
• Assuming the whole tower has one IP rating. The listed sounder is IP66 while the LED modules are IP67. On a wash-down line, a module not rated for the clean-down can be the first part to fail. Check the rating of every module, not just the base.
• Leaving the cable entry until install day. A 1/2 inch NPT entry does not take a standard metric gland on its own, so the electrician ends up improvising on site. Decide the entry type when you order and have the right adaptor in the van.

Frequently Asked Questions

Choosing the build

Is a pre-assembled signal tower base easier than building the stack?

For a straightforward job, usually yes. The pre-assembled 24V signal tower base comes as a ready unit with a 1/2 inch entry, so you are not matching parts one by one. Build from separate bases and modules when you need a mix that a complete tower does not offer.

What does IP67 mean on a signal tower?

IP67 means dust-tight and protected against temporary immersion in water. It rates the enclosure, not the cable entry, so a poorly sealed gland or conduit fitting can still let water in. Check each module's rating, because a sounder can be rated differently.

Wiring and mounting

Does a signal tower need a licensed electrician to install in Australia?

If it is wired to 240V AC, yes. Fixed wiring at that voltage must be done by a licensed electrician. Rules for 24V extra-low voltage work can vary by state, so check with your local regulator if you are unsure.

Can I connect a 1/2 inch NPT signal tower base to metric conduit?

Not directly in most cases. NPT and metric threads are not interchangeable, so you typically need a thread adaptor or the M20 tube base. For mounting on a 1/2 inch NPT thread, Schnap lists a 1/2 NPT mounting base adaptor. Check the datasheet for how it fits your base.

Modules and spares

Can I mix steady and strobing modules on one tower?

Typically yes. Each module sits on its own circuit, so you can stack different types in the order the operator needs to read them. Confirm module voltage and circuit count against the datasheet before ordering.

Can I replace a cracked lens on a 70mm tower light?

You may not need a whole new module. A replacement lens diffuser kit is listed for 70mm tower lights. Check the part code against your module before ordering.

Shop Signal Tower at Schnap

Here is the signal tower range discussed above, with trade pricing and same-day dispatch from Kingsgrove NSW.

Complete signal towers

• 240V AC 3-circuit signal tower, 60cm pole, IP67
• 240V AC 7-circuit signal tower, 60cm pole, IP67
• 24V AC/DC signal tower, 40cm pole, IP67
• 240V AC 2-element signal tower, IP67

Bases

• Pre-assembled signal tower base, 24V AC/DC, 1/2 inch, IP67
• Stack light base, 240V AC, 25cm M20 tube, 70mm, IP67
• Stack light base, 240V AC, 7-circuit, 1/2 inch NPT, vertical mount, IP67

Modules

• Steady LED module, green, 70mm, 24V AC/DC, IP67
• Rotating LED module, 70mm, 24V AC/DC, IP67
• Strobing LED module, 70mm, 24V AC/DC, IP67
• Sounder module, 70mm, 102dB, 8-24V AC/DC, IP66

Mounting and accessories

• Mounting base adaptor, 250mm pole
• Vertical mount base adaptor
• Mounting base adaptor, 1/2 NPT
• Replacement lens diffuser kit, 70mm tower light

Browse the full signal tower range at Schnap.