Understanding UL and NFPA

Correct construction of industrial control panels and electrical equipment bound for export to the USA

Schaltschrankbau, Author Jürgen Werning

Most of the machines and equipment produced here in Germany are bound for export. Although this mainly concerns IEC standards and European directives, second place goes to the USA, where close attention is paid to compliance with the entire spectrum of local standards and regulations. One thing is extremely important when it comes to implementing such rules and working together with the local supervisory authorities: you have to keep abreast of developments. Support is available to ensure that the way you design and configure your control panels and electrical equipment for machines complies with UL and NFPA requirements.

The Machinery Directive 2006/42/EC – formerly known as 98/37/EC – the Low Voltage Directive (2006/95/EC) and, as of April, the new 2014/35/EC are among the key reference points for German machinery and equipment manufacturers when it comes to electrical equipment. However, what applies in Europe is often only of marginal significance for global markets. In the USA, for example, UL 508 A (Industrial Control Panels) issued by the Underwriters Laboratories and the NFPA 79 standard from the National Fire Protection Association constitute the reference works for electrical installations alongside the National Electrical Code. These are the standards by which US supervisory authorities evaluate the reliable operation of machinery and equipment in terms of electrical safety. It is important to clearly recognize the differences between IEC on the one hand and UL and NFPA on the other.

However, anyone who is not a professional in the field of standards needs solid specialist support to make sure that problems do not emerge when machinery and equipment are delivered to and eventually commissioned in the USA. Put another way: those who know the American standards jungle down to the last detail and are in a position to implement everything in compliance with the rules are themselves already true professionals – or they have received professional support.

Three-day seminar on UL and NFPA

The Siemens experts know just how important it is to offer ongoing training on the subject of US standards. That is why they have developed in-service training courses that have proved very popular among the target group. In the meantime, the one-day events have been turned into a three-day seminar offering everything participants need to know about exporting to North America – from basic knowledge through to a practical workshop.

One brand new element, for example, is the practice-oriented, graphic configuration of an imaginary industrial machine. This excursion into the world of UL concentrates on the selection and design of suitable components and includes their dimensioning in the main and control circuits. Like the other two modules, this new, third advance training module can also be taken separately. Such a three-day training program, in which participants start from the basics and end up configuring their own equipment, not only imparts a lot of knowledge to employees working with standards but also gives them more confidence in handling their own day-to-day business.

Meet the requirement – or face a plant outage

This is an important point because once the equipment is installed overseas, any modification to the machinery or equipment could become a costly and time-consuming exercise – however minor the modification may be. There is one thing we always need to bear in mind: every industrial plant needs an operating permit from the authorities, whereby compliance with and enforcement of codes and standards is overseen by the government. Requirements are issued by three different bodies:

  • Federal government: These requirements can be met by original equipment manufacturers themselves by basing their approach on IEC 60204-1/IEC 61439-1, as these are substantially comparable with the US standards.
  • State government: These requirements are based on the individual stipulations in the specific states of the USA. For example, one state may implement versions of standards that have already been superseded by newer versions in other states. The latest edition of the NEC (National Electrical Code) for instance, which was issued in 2014, is not yet applied in every state.
  • Local government: It is almost impossible to delegate these requirements to the OEM. They are based on special aspects such as environmental constraints. Local "city codes" may be applied that set out specific additional requirements.

Whatever the authorities having jurisdiction say is "law"

Whenever possible, the end-user should be consulted at the outset regarding the local requirements issued by the authorities having jurisdiction (AHJ) – for example the State Electrical Commissioner or State Fire Marshal – and such requirements should be met. "There is no chance of a trouble-free acceptance procedure without National Electrical Code (NEC) (NFPA70) in general or UL508 A, UL508C/UL2011 in particular."

Machinery and equipment manufacturers have to make sure that they comply with every detail of the latest standards. There is nothing worse than out-of-date standards – whether here in Europe or in the USA. The end-use application determines the standard to be applied. It is therefore important to know some essential details, such as the structure of the line system, when designing industrial control panels and electrical equipment. There are many different line system configurations in the USA, which is why exact assignment regarding slash or delta ratings are of vital importance. This is also one of the relevant points in UL 508 A. Furthermore, in connection with the Conditions of Acceptability (CoA), it is important to make sure that the components used are really approved for the application concerned – that is to say whether they are UL-listed or UL-recognized.

Many differences in details compared to the IEC standards

These and many other hurdles must be known and correctly overcome. For example, UL 508 A applies to industrial control panels with a voltage up to 600 V for normal ambient conditions. In practice, the standard sets out rules for all important points, from the power infeed to the terminals of the outgoing feeder panel. On the other hand, NFPA 79 is the relevant standard for electrical components in industrial machines and equipment up to 600 V for normal ambient conditions. It applies from the power infeed through to the individual machine modules and is intended to protect both personnel and equipment.

Those who have attended the three-day UL seminar are familiar with the key aspects of standard-compliant industrial control panel manufacture for North America. UL 508 A states specific rules for the ability of the industrial control panel's main circuit to withstand short circuits, whereby an industrial control panel must be marked with an SCCR (short-circuit current rating).

The rules concerning the industrial control panel's infeed are different from those of the IEC, as are the requirements regarding miscellaneous consumers and loads. In contrast to the IEC world, circuit breakers according to UL 489 or fuses according to UL 248-4…12 usually have to be used for these applications. The equipment manufacturer's UL report determines the choice of protection for motor loads on a case-by-case basis. A type F motor starter is typical here, that is to say the combination of motor circuit breakers and contactors tested by the manufacturer.

What protective mechanisms are used and where depends on the type of main circuit – whether it is a feeder circuit or a branch circuit. However, the control circuit does not belong to either of the two – other rules apply here. According to UL 508 A, a control circuit is normally limited to 15 A. On the other hand, there are also control circuits with limited energy (low-voltage limited energy circuits) for which the current is restricted to 5 A and the power to 100 VA. However, the actual design of control circuits can vary tremendously. According to UL 508 A, there are also many rules to be observed regarding UL-compliant marking of the industrial control panel from the rating plate through to the marking of the wire-ends.

NFPA 79 also applies outside the industrial control panel

There are also a great many differences to the European "way of life" regarding NFPA 79, the standard for electrical safety for the machine as a whole – both inside and outside the industrial control panel. The field wiring, i.e. installation of wiring outside the industrial control panel, is just as clearly regulated as the selection of the motors in the field. Labeling, safety notices and technical documentation round off the content of NFPA79.

However, as far as machine safety is concerned, it refers the reader to other standards such as IEC and ANSI. Unlike UL 508 A, NFPA 79 prescribes various tests and specifications that have to be applied. The stipulations regarding control elements such as pushbuttons, emergency stop buttons, etc. are also very detailed. Installation location, assembly and distances in the work zone are exactly specified in the standard. Once more, there is a series of stipulations to be observed concerning infeed, main switch, lighting, motor protection, equipment protection and a whole lot more.

Making effective use of advanced training opportunities

An initial glance at the content of the two key standards relevant to the manufacture of machinery and equipment destined for North America – UL 508 A and NFPA 79 – shows that, when it comes down to detail, there are major differences to the standard-compliant design of industrial control panels and electrical equipment in Europe. And so it seems advisable to make good use of the advanced training opportunities available on the market in order to avoid potential difficulties when supplying and commissioning machines and equipment in the USA.

Anyone wishing to supply industrial control panels and electrical equipment to North America should have very good knowledge of the UL 508 A and NFPA 79 standards if they wish to avoid potential problems. Source: Siemens AG