Schneider / Harmony control and signalling

A red mushroom head is not automatically an emergency stop. Only the trigger action versions carry the standards, and they are a specific part number.

Harmony is the Schneider 22 mm control and signalling range. Pushbuttons, selector switches, pilot lights and emergency stops, in every panel in the country.

XB is assembled, ZB is components

The thing to understand first, because it decides what you order.

A worked example. XB4BA31, a green flush pushbutton with one normally open contact, is made up of:

So XB4BA31 and ZB4BA3 plus ZB4BZ101 are the same thing, ordered two ways.

Which is right for you

Order the XB assembled unit for a new panel or a straight replacement. One line, one part, ready to fit a 22 mm cutout.

Order ZB components when only one half has failed. A cracked or faded head with a perfectly good contact block underneath is a head order, not a whole unit.

That is worth asking about. Heads take the abuse and contact blocks usually do not.

XB4, XB5 and XB7

XB4 and XB5 are the same function in metal or plastic. Metal for harsh environments and where the panel takes knocks; plastic where cost matters and the environment is kind.

They look similar from the front and the heads are not interchangeable. A ZB4 head does not go on a ZB5 body. Check the existing unit rather than matching on appearance.

Some current contact blocks are specified as compatible with both ranges. If you are mixing, tell us and we will confirm.

Emergency stops: trigger action is the requirement

The most important thing on this page.

Schneider is explicit that mushroom head emergency stop trigger action and mechanical latching pushbuttons conform to:

The trigger action versions are specific references. Schneider identifies them as XB4B*8*** and XB4BS9*** in the metal range, and XB5A*8*** and XB5AS9*** in plastic.

A red mushroom head that is not a trigger action version is a pushbutton with a red mushroom head. It may look identical in the panel and it does not carry the emergency stop conformity.

If you are replacing an emergency stop, match the exact reference. If you are specifying one, tell us it is an emergency stop and we will quote a trigger action unit.

Why trigger action matters mechanically

Worth understanding, because it explains why the distinction is not bureaucratic.

A trigger action contact block opens the circuit by direct mechanical action, independent of spring force and independent of whether the contacts have welded.

An ordinary pushbutton relies on a spring to return and open the contact. If that contact welds, an ordinary button can be pressed and the circuit stays made.

That is the failure mode the standards exist to prevent, and it is why the reference matters more than the appearance.

As with every safety part on this site: we supply what you specify, and whether a substitution is valid for your machine's safety function belongs with whoever holds the assessment.

The RA suffix, and why it exists

A neat problem and a neat solution, and it catches people fitting into tight panels.

Schneider notes that heads are fixed relative to the position of the contact blocks, and contact blocks are normally used in the vertical position.

If you need to mount the contact block horizontally, because of space behind the panel, you cannot just turn the assembly. The symbol on the front would end up rotated.

So Schneider offers alternative heads with the symbol rotated by 90 degrees. Add the suffix RA to the reference.

An RA head with a standard guard will not work. Schneider specifies the ZBZ1902RA guard for RA heads, and that is a separate order line.

So if you are short of depth behind a panel, RA is the answer, and it is two parts rather than one.

The figure 7

An ordering modifier that appears throughout the Harmony catalogue and looks like a typo when you see it in a parts list.

Schneider instructs: to order, add a figure 7 to the references selected above. The examples given are:

The modifier relates to the terminal connection type, with Schneider's screw clamp anti-retightening system noted alongside it.

The practical point: send us the reference exactly as it appears, trailing 7 included. Dropping it gets a different connection type, and adding one that should not be there does the same.

Illuminated units need a voltage

An incomplete reference is a common cause of a wrong order.

Schneider notes that for illuminated units the basic reference must be completed, either by adding a letter B, G or M for the voltage, or by replacing a placeholder with 1, 2, 3 or 4, depending on the range and catalogue.

So a reference for an illuminated pushbutton or pilot light is not complete without the voltage character. If a parts list has one missing, that is why the order cannot be placed as written.

Tell us the control voltage and we will complete it.

Lamp base fitting is BA 9s, maximum 11 mm diameter and 28 mm length.

There is a limit on contact blocks per head

Schneider publishes a recommended maximum number of contacts constituting the body, meaning the fixing collar plus contacts, for each head.

You cannot keep stacking contact blocks indefinitely. The head has a mechanical limit on how many it can reliably operate.

If a circuit needs more contacts than one unit allows, that is an interposing relay rather than another contact block. Tell us how many contacts you need and we will check it against the head.

Interposing relays are covered on our Zelio relays page.

Other useful details

The panel thickness restriction is worth checking on a thick door. And note the same versions cannot take legend holders, so if you need labels you need a different variant.

The 22 mm cutout is an industry standard, so a Harmony unit fits a hole cut for another brand. That makes Harmony a practical replacement where an obsolete control device cannot be sourced, provided the contact arrangement matches.

Before ordering a replacement

What to send us

The full reference including any trailing 7 or RA suffix.

Whether you need the complete unit or just the head or contact block.

For illuminated units, the control voltage.

For an emergency stop, say so, because that determines a trigger action part.

XB4 metal or XB5 plastic, since they are not interchangeable.

A photo of the front and the back of the existing unit resolves most of this.

What we can supply

Current production. XB4, XB5 and XB7 complete units, ZB4 and ZB5 heads, bodies and contact blocks, emergency stops, selector switches, pilot lights, legends, guards and mounting accessories. Quoted with a delivered lead time.

Bulk. Control devices are a panel-build consumable. Send us the schedule and we will quote the lot.

Heads and blocks separately. Often the cheaper repair.

Discontinued. Earlier Harmony and Telemecanique control devices. Surplus where available.

Other brands. We also supply Siemens SIRIUS ACT, Allen-Bradley 800F and 800T, and Omron A22 control devices. We have not published reference tables for those ranges, so send us the part number and we will quote it.

Related

Schneider overview, Zelio relays for interposing, Preventa safety for the relays an emergency stop wires into, TeSys contactors and Magelis and Harmony HMI.

For emergency stop devices from other brands see Allen-Bradley Guardmaster, which covers the 800F and 800T bulletins, and Pilz for PIT operator devices.

Send us your references

Exactly as written, including trailing characters. If a reference looks incomplete, it probably is, and it is usually a missing voltage character on an illuminated unit. Quotes in NZD including GST.

Request a quote

Industech is an independent supplier of new, surplus and used industrial automation equipment. We are not an authorised distributor of, approved by, sanctioned by, or affiliated with Schneider Electric. Schneider Electric, Harmony, Magelis, Vijeo and Telemecanique are trademarks of Schneider Electric. All trademarks, brand names and references are the property of their respective owners and are used here for identification purposes only. Information on this page is for identification and does not constitute a safety assessment.