Wireless Remote Installation: Pairing, Relay Wiring and Safety

Why is factory-set coding safer than DIP switches for receiver-transmitter pairing? Why should a 2×10 A relay never drive a DC motor directly? Passive stop timing, mandatory interlocks, 433 MHz duty cycle and antenna placement — with the calculations.

Installing a wireless remote sits at the intersection of three disciplines: the radio side (band, power, duty cycle), the safety architecture (passive stop, addressing, emergency stop) and power switching (relay, contactor, interlock). Neglecting any one of the three makes the other two meaningless. This article covers all three with concrete numbers.

Which standard binds what?

Pairing: factory code or DIP switch?

IEC 62745 requires that operating command signals "affect only the intended base station or remote station (for example by using an address code)" and that at that station they "initiate only the intended functions". The note in the same clause of the standard states a preference that the industry often skips:

Typical methods are factory-set coding; it is more robust than user-configurable methods, because it cannot be defeated by the user (intentionally or accidentally).

If addressing is done with DIP switches, additional measures such as parity checking may be required to meet the requirement under fault conditions. Practical conclusion: learn-in, factory-coded pairing should be preferred, every receiver-transmitter pair on the same site should be given a unique address, and this list should be recorded.

Other concrete requirements of the standard:

• If unauthorized use must be prevented, a key switch or access code must be provided (cl. 4.2.2).
• Unintended actuation (dropping, striking an obstacle, electronic failure) must be minimized by design (cl. 4.2.1).
• An easy means of stopping transmission must be provided; removing the battery without tools is one of the three methods accepted by the standard (cl. 4.4).
• Re-energization: switching the remote on, changing the battery or re-establishing communication after signal loss must not activate any hazardous output.
• Serial data transmission: for the probability of an erroneous frame being accepted undetected, a Hamming distance ≥ 4 (or the number of frame bits divided by 20, whichever is greater) or an equivalent error probability criterion must be met.

Passive stop: what must happen when the remote goes silent?

IEC 62745 defines passive stop as a safety-related stop caused by the absence of a valid signal at the base station, and lists as triggers going out of range, battery failure and electromagnetic interference. EN 13557 Annex C.3.2 defines the maximum permitted duration of signal absence for cranes as 0.5–2 seconds.

On the safety architecture side, EN 13557 Annex C requires at least Category 3 for the stop function of a wireless remote — a single fault must not cause loss of the safety function. Levels achieved in practice on certified industrial crane radio remotes: manual stopping via the mushroom button PLe, automatic stopping when the radio link drops PLe, prevention of unexpected start PLd.

The honest warning that follows: a general-purpose two-relay receiver with a single-channel stop cannot reach this level. A lifting machinery application requires a separate, dual-channel safety stop output.

Stop categories

With a suspended load on a crane the typical choice is Category 0, and the brake must be spring-applied. On drive/inverter systems Category 1 is preferred to reduce load sway.

The radio side: band, power, duty cycle

In Turkey, licence-exempt use is defined by BTK technical criteria. The rows relevant to a remote control application:

What a 10% duty cycle means in practice: 1 hour = 3600 seconds, so a maximum of 360 seconds of transmission. Since a crane remote transmits for as long as a button is held, a single continuous maneuver longer than 6 minutes runs into the band limit. Commercial remotes therefore lower the average duty cycle through packet structure and neutral frame intervals.

Why still 433 MHz?

Wavelength is λ = c / f. The free-space path loss difference is 20·log₁₀(2441 / 433.92) = 15.0 dB. That is, at the same distance 2.4 GHz drops roughly 15 dB more than 433 MHz. Diffraction capability also scales with wavelength: at 433 MHz λ ≈ 69 cm, so the signal can bend around the edge of a column and reach the shadow region; at 2.4 GHz λ ≈ 12 cm, so the same obstacle creates a much sharper RF shadow. This is why 433/868 MHz is preferred for field remote control.

Antenna placement: the real determinant of range

A fully metal enclosure behaves like a Faraday cage and blocks nearly all RF energy; an internal antenna only works if there is a deliberately provided RF-transparent window. That is why with in-panel receivers (e.g. LF100R) the antenna must always be brought outside the panel.

Rules to apply in the field:

1. Bring the antenna outside the panel and orient it vertically.
2. Keep it at least λ/4 away from any metal surface (~17 cm at 433 MHz).
3. The metal panel cover can be used as a ground plane; the antenna base should seat on the cover with good galvanic contact.
4. Keep the antenna away from the frequency inverter, contactors and motor cabling.

Fresnel zone: the "I can see it, so it must have signal" fallacy

The radius of the first Fresnel zone is r₁ = 8.657 · √(D / f) (D in km, f in GHz, result in meters). The rule: at least 60% of this zone must be clear.

So on a 100-meter link, the volume from the ground up to roughly 4 meters at the midpoint of the path is the "radio volume". Placing the receiver antenna close to the ground or behind a stack of pallets degrades the link even with optical line of sight.

Relay output: dry contacts and the difficulty of DC

A dry contact is a potential-free contact that carries no voltage of its own through the relay and only opens and closes an externally supplied circuit. The receiver's 2×10 A relay output is of this type: the receiver is powered from 12/24 V DC or 220 V AC, but the relay contact switches an independent circuit.

Fail-safe rule: Control channels must use NO (normally open) contacts — if the receiver loses power, motion stops by itself. The brake and safety chain, on the other hand, must be built on NC (normally closed) contacts so that a break also leads to a stop.

Why is "10 A" not 10 A on a DC motor?

In AC the current crosses zero 100 times (50 Hz) or 120 times (60 Hz) per second and the arc extinguishes naturally. In DC the current never reaches zero naturally; the arc persists until the contacts fully separate. The result:

Furthermore, the permitted current collapses rapidly as voltage rises: at 40 V DC the permitted current drops below 2 A. The arc initiation threshold depends on the contact metal — on fine silver it is around 12 V / 0.4 A.

Contact protection

On DC loads the most effective method is a diode, followed by an RC element; on AC loads a varistor or RC is preferred. RC snubber sizing: R = 0.5–1 Ω per contact volt, C = 0.5–1 µF per contact ampere. For a 24 V, 5 A inductive load: R = 12–24 Ω, C = 2.5–5 µF.

Critical warning: a flyback diode connected in parallel with the load eliminates the back-EMF, but it extends the release time of the connected relay, solenoid or clutch. In a crane brake or emergency stop chain this delay may be unacceptable; there, a diode + zener or a varistor is used instead of a plain diode.

Interlock: why forward-reverse locking is mandatory

If the forward and reverse contactors pull in at the same time, a short circuit occurs. Industry practice is to use two layers together:

What to do at the relay output level:

• The receiver relays must not drive the motor directly; they must drive contactors.
• If channel 1 = forward contactor coil and channel 2 = reverse contactor coil, a mechanical interlock block must be fitted between the two contactors and the mutual NC auxiliary contacts must be wired in series.
• The software logic inside the receiver that "two channels must not be active at once" is not sufficient on its own; it is a single point of failure.

Number of interlocks on multi-channel sets

Running manual pushbuttons in parallel with RF

Commissioning an RF remote while keeping the existing pushbutton wiring is a fast and low-risk modernization — but it triggers the multiple control stations and control suspension clauses of IEC 62745. If two control sources are active at the same time, it must be defined which one has priority; otherwise a risk of unexpected motion arises. This priority logic must be documented during installation.

Installation checklist

1. Prefer factory-coded / learn-in pairing; if DIP switches are present, require additional verification.
2. Assign a unique address code to every receiver-transmitter pair on site and record it.
3. Add a key switch or access code against unauthorized use.
4. Place the antenna outside the panel, vertically and ≥ λ/4 away from metal.
5. Keep 60% of the first Fresnel zone clear along the link.
6. Use the relay outputs as NO; let them drive contactors, not the motor.
7. Fit mechanical + electrical interlock on the forward/reverse contactors.
8. Use a flyback diode or RC snubber on inductive loads — watch out for release delay in the brake circuit.
9. Measure the passive stop time: when the remote is switched off, motion must stop within 2 seconds.
10. Emergency stop test: with a suspended load, press the mushroom button → does the brake hold?
11. Battery change test: when the battery is inserted, no output may activate by itself.
12. Out-of-range test: the machine must stop when the operator walks to the limit, and must not restart by itself when he walks back.

What is in the AXI sets?

On rechargeable remotes, battery management is also a safety matter: IEC 62745 lists battery failure directly as a passive stop trigger. The correct design rule is this — a low battery must not silently degrade into weak transmission; it must warn and then cut transmission in a controlled manner. Gradual range shortening on a weak battery leads the operator to walk into a hazardous distance without noticing.

Related content

• How to Pair a Crane Remote Transmitter and Receiver
• 433 MHz or 2.4 GHz? Choosing a Frequency for Crane Remotes
• Complete Guide to IP Ratings: What IP54, IP64, IP66 and IP67 Actually Measure

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