LVD Voltage Limits are RMS + Thoughts on Marginal Voltages

The LVD a.c. voltage limits are defined in terms of rms. From 2014/35/EU

This Directive shall apply to electrical equipment designed for use with a voltage rating of between 50 and 1 000 V for alternating current and between 75 and 1 500 V for direct current

So that’s 50Vrms and 1000Vrms.

 

Example

A customer was asking about a low current (sub 1mA) 40Vac rms source and if the LVD applied.

This voltage is less than the 50Vrms threshold mentioned above so would be technically exempt from the LVD. Unless of course the equipment contained a radio module in which case the RED makes the LVD applies with no lower voltage limit.

I think that there is still a risk that needs to be assessed here.

Just because you are exempt from the directive doesn’t mean you are exempt from making your product as safe as possible.

 

Looking at the main table from 62368-1 for categorising shock risk, 40Vrms/50Hz means it is an ES2 hazard. The voltage source would have to be under this limit for normal operation, abnormal operation (e.g. blocked vent, stalled motor, controls set incorrectly) and single fault (open/short circuit) conditions.

 

This means, even though the LVD is not strictly not applicable, it would be wise to put in a Basic Safeguard between the user and the exposed voltage.

Additional: The provisions of the General Product Safety Directive (2001/95/EC) would apply to any product falling outside of any specific safety standard. The Harmonised Standards for this Directive include EN 60065 and EN 60950-1. Since both of these have been superseded by EN 62368-1 it would be reasonable to use this standard instead.
Thanks to Charlie Blackham from Sulis Consultants for the tip.

This safeguard could be an enclosure, insulation, an interlock or barrier.

Instructions or PPE aren’t sufficient as they are considered supplementary safeguards.

 

But what about the current limits?

That’s just considering the voltage source purely from a voltage perspective. If it can’t drive enough current into a 2000 ohm load for more than 2 seconds to form a hazard then that might change the classification.

This current is measured using one of the appropriate networks from EN 60990 such as the one below

 

 

But I know what I’m doing…

The requirement for safeguards depends on if you classify the user as a normal person or an instructed person

Skilled person > instructed person > normal person

3.3.8.1 instructed person
person instructed or supervised by a skilled person as to energy sources and who can
responsibly use
equipment safeguards and precautionary safeguards with respect to those
energy sources

3.3.8.2
ordinary person
person who is neither a skilled person nor an instructed person

3.3.8.3
skilled person
person with relevant education or experience to enable him or her to identify hazards and to
take appropriate actions to reduce the risks of injury to themselves and others

The level of safeguard required between the user and the ES2 hazard is defined in EN 62368-1

For a normal person we must use a basic safeguard

But for an instructed person we may use a precautionary safeguard

A Precautionary safegard (defined in 0.5.5.3) could take the form of instructions or training, but the addition of warning stickers, PPE could also be considered part of this.

 

Summary

This is why I like EN 62368-1 over some of the older safety standards (I’m looking at you, 60950)

Rather than a prescriptive “thou shalt use 2.5mm clearance or be smote verily” it helps and guides you through all the steps into understanding why or how a requirement is derived.

Also the companion EN 62368-2 explanatory document contains even more background and context. I wouldn’t recommend applying -1 without having -2 to hand.

Stay SAFE kids.