Wylex NHXS1B20 RCBO B Curve 20A 30mA Type A

In-Depth Look

The shift from split-load consumer units to full RCBO boards has been one of the most significant changes in UK domestic electrical installations. An RCBO board gives every circuit its own earth leakage protection, eliminating the problem of a single fault tripping half the house.

Why RCBOs

In a traditional split-load board, circuits are grouped under shared RCDs. A fault on any circuit in the group trips the RCD and disconnects every circuit in that group. With RCBOs, each circuit has independent protection: a fault on the kitchen ring only affects the kitchen ring, not the lighting, sockets, and everything else on the same RCD.

B Curve Rating

The B curve trips instantaneously at 3 to 5 times the rated current, making it suitable for resistive and lightly inductive loads: standard socket outlets, lighting circuits, and immersion heaters. A C curve device is often chosen for equipment with high inrush current, such as some motor-driven equipment; the designer decides.

Verdict

The Wylex NHXS1B20 is an RCBO for Wylex NM and NMX consumer units; check compatibility against the Wylex data sheet. RCBO boards are a common choice, split-load boards are still permitted, and the single-module width means a full RCBO board does not require a larger enclosure than a traditional split-load design.

How It Compares

The Wylex NHXS1B20 is a 20A RCBO with 30mA earth leakage protection in a single 18mm module. An RCBO combines an MCB (a miniature circuit breaker, which protects against overload and short circuit) and an RCD (a residual current device, which cuts the power if current leaks to earth) into one device protecting one circuit. The product information lists it for a particular Wylex consumer unit range, so check that range against your board.

Hager, Schneider and Eaton all make RCBOs for their own consumer units, and this site has a page for the Chint RCBO (chint-rcbo-type-a-b16). On paper many look alike, with the same current rating and 30mA sensitivity. The real difference is the board they are designed to fit.

That is the main compatibility trap. RCBOs are made to fit a particular manufacturer’s busbar and enclosure. The product information says this one is compatible only with a specific Wylex range, so you cannot assume it will fit another make, or even a different Wylex range. Check the part code against the consumer unit’s manual before you order.

The wording on the product page can be confusing, so here is the clear version. The “B” in the model name refers to the MCB trip curve, which describes the level of overcurrent at which the MCB part trips quickly. The RCD part has its own type marking, such as AC or A, shown on the device. Retailer listings generally show this part as a Type A RCD with a B curve MCB, but read the marking on the device you receive. They are different things.

A single RCBO on its own is not a design decision. Which devices go on which circuits, and which type of board suits the property, is for a qualified registered electrician to decide under current regulations.

Common Questions

Can I fit this RCBO in a different make of consumer unit? Do not assume so. RCBOs are usually designed for one manufacturer’s board, and the product information lists this one for one Wylex range only. Mixing makes can affect fit, performance and the board’s approval. Ask a qualified registered electrician, and check the consumer unit manufacturer’s list of compatible devices.

What does the 20A rating mean for the circuit it protects? The rating is the current the device is designed to carry before it responds to overload. It must be chosen to suit the cable and the load on that circuit. The right rating for a particular circuit is part of the circuit design, so leave that decision to a qualified registered electrician.

What does the B in the name mean on this RCBO, compared with the Type A or AC marking? Two different labels are in play. The B in the name refers to the MCB curve, meaning how it reacts to overcurrent. Type AC, A, F and B on the RCD side describe what kinds of leakage current it detects. This product’s listing describes the overcurrent curve, so read the device marking and data sheet for the RCD type.

What should I do if the RCBO keeps tripping? Do not keep resetting it or swap it for a larger rating. A trip is the device doing its job. Try unplugging appliances on that circuit, as a faulty appliance is a common cause, and then reset once. If it trips again, stop and call a qualified registered electrician to investigate the circuit.