If the voltage increases beyond the design limit, the diode goes into avalanche breakdown, causing the harmful voltage to be conducted to ground. When used in this fashion, they are often referred to as clamping diodes or transient voltage suppressors because they fix or "clamp" the maximum voltage to a predetermined level. Avalanche diodes are normally specified for this role by their clamping voltage VBR and the maximum amount of transient energy they can absorb, specified by either energy (in joules) or i 2 r t {\displaystyle i^{2}rt} .