Should appliance outlet be regarded as multiple socket-outlet?

[Roland chung]

Hi all,

When an IEC 60320 appliance outlet is used to construct an ME system, does clause 16.9.2.1 (multiple socket-outlet) apply?

- If applies, the appliance outlet which is IEC 60320-2-2 approved already would be required to comply with IEC 60884-1 also. It seems to me unreasonable.

- If not, there would be no requirement for classification of multiple socket-outlet. According to 16.9.2.1 c), second dash), only Class I construction is allowed. I would think Class II appliance outlet should not be used.

Furthermore, I am very confused about the 16.9.2.1 c), second dash. Does this mean that multiple socket-outlet mounted on Class II ME equipment without functional earth (Class II ME equipment is an item of the ME system) shall also be Class I construction? Or does the standard reject the Class II ME equipment without functional earth to construct ME system by means of multiple socket-outlet?


Please help to clarify. Thank you very much!

Roland

 

[Pads38]

Hi Roland,

To begin with I thought that this might be a straight forward question but it does seem rather more involved.

To begin with from the rationale of Annex A -

Subclause 3.67 Multiple Socket Outlet
A single socket-outlet forming part of an equipment is also considered a MULTIPLE SOCKET OUTLET (MSO)

- so your example falls within that definition.

Now from the 'Scope' of IEC 60884 -

This standard does not apply to
? plugs, socket-outlets and couplers for industrial purposes;
? appliance couplers

- so I would suggest that your socket, as an appliance coupler, should conform to IEC 60320 only.

If an un-earthed MSO was available there is a clear risk if someone plugged in something that demands protective earthing. This situation must be avoided, hence the requirement.

I could see you may be able to say that this requirement is Not Applicable if the connection to the outlet could only be made after use of a tool (say if it was an internal connection that could not normally be accessible.

 

[Roland chung]

Thank you very much for your insights.

But the definition of MSO is derived from IEC 60884-1 (see subclause 3.67 rationale), so my instinct is that appliance coupler should not be regarded as MSO. They are just two different things. So, the clause 16.9.2.1 is not applicable.

 

[Peter Selvey]

Without reading the detail in the standards: the concern with a general purpose MPSO is that users will build an ad-hoc ME system without checking everything is OK, such as checking for cumulative leakage currents.

An IEC 60320 outlet is not a common type so it is unlikely that a user will build an ad-hoc ME system. In practice, the manufacturer will usually supply a special cable for a particular accessory, so the ME system is effectively fixed and can be evaluated under Clause 16. In that context, Class I or Class II is irrelevant.

 

[Roland chung]

Thank you, peter.

One argued that interconnection couplers are not that unusual. User can easily get such interconnection cable from shop. That means the ME system is not fixed. So Class I IEC60320 outlet should be used.

For ME system constructed as shown in Annex I Table I.1, item 1C (ME and non-ME equipment are connected to mains supply separately), the Touch Current will not be additive in SFC if both devices are Class I (even if earth conductor of non-ME is interrupted, the leakage current will flow from the non-ME into the earth conductor of ME equipment via the functional connection between ME and non-ME equipment). So no additional protective earth connection or separating transformer needed. Am I correct?

Regards,
Roland